How far back from the frame rails should you go for habitat?

[driveby]

Tumbling ideas around my head. Assume a F550/5500 crew cab chassis truck with a custom frame mount. Something like a Total Composites box on top and proper SRW conversion with something like Liquid Springs and 2" lift and 42" GoodYears etc.

Use case: casual off road - bad forestry roads, washboard, drainage ditches from Baja to Yukon (west BLM/Crown land etc.) 2 humans, no dogs, lots of outdoor hiking, kayaking. Living inside as we work remotely and go out for a couple hours of hiking/kayak and then back to living normally. IE we want to be out in the rain/snow/cold/heat to explore but not have to be to eat or relax or work. A comfortable hi/lo table (work desk and food) and dry shower to hang wet drysuits and goretex jackets. Largest cooking area as we like to cook. More than just one sitting space. You can see my dilemma - interior space is at a premium. We started thinking ~40' Class A but then realized that limits our places to access too severely. So now we're on a march to how small is too small and how large can we go before we might as well go back to that Class A and park at RV parks....

I'm doing some interior space planning, the more space the merrier. But what I can't find is how far aft of the factory frame is too far? I won't have anything more than chairs/bbq/folding kayaks in the rear storage/garage so weight probably isn't my enemy. I think the rear departure angle will ultimately be my limiting factor. Attached are my kindergarten level GA plan and side views. Sorta to scale(ish). Dinette seats would be 24-30" (single person + a bit of wiggle room) and as much kitchen counter space as we can squish in with overhead cabinets for storage.

 

[carleton]

That's the dream scenario, right?!?

I was doodling something similar a few years ago, I think I needed a 9-10 foot box inorder to actually squeeze in what I wanted to get in there.


Victorian probably has some advice on mounting a TC box, but not sure you'd want to get behind the frame too much, since that portion of the vehicle then becomes a bumper in a rear-end accident.
Vehicles like the RossMonster Baja end at the frame, then have an agressive departure angle (really to lengthen the interior more)
The Baja - Rossmonster Overland
.

 

[Victorian]

Ford has a guide that tells you the maximum sizes for each chassis. Follow that and you will be fine.
home

 

[1000arms]

Assume a F550/5500 crew cab chassis truck with a custom frame mount. ... I'm doing some interior space planning, the more space the merrier. But what I can't find is how far aft of the factory frame is too far? I won't have anything more than chairs/bbq/folding kayaks in the rear storage/garage so weight probably isn't my enemy. ...

You might want to consider a regular cab for the two of you. There are longer CA (Cab to Axle) frame lengths available on 2023 Ford 450/550/600 regular cabs than there are on crew cabs (and the 2023 F-600 only comes in regular cab). See the following link and click on "specifications". https://www.ford.com/commercial-trucks/chassis-cab/models/f550-xl/

There are also "aft-axle frame extensions" available to order on 2023 F-450/550/600 regular-cab chassis-cabs with with CAs of 60" and 84". The "aft-axle frame extensions" are designed for lighter equipment at the end of a truck, but keep the wheelbase shorter than going to a longer CA. They would probably work well for your needs (other than impacting departure angle). I think the cost to add the "aft-axle frame extensions" option to a 2023 chassis-cab "build and price" order is $115 USD. See the above link and click "specifications". Also check the following link and look for "aft-axle frame extensions". https://www.ford.com/commercial-trucks/chassis-cab/features/durability/

A 2023 regular-cab chassis-cab f-450/550/600 with 84" CA and "aft-axle frame extensions" is about 3" shorter than a 2023 regular-cab chassis-cab f-450/550/600 with 120" CA, but has a 169.5" wheelbase rather than the 120"CA's 205.3" wheelbase. ... Both are about as long as a 2023 crew-cab long-bed pickup truck with the tailgate down, but the 2023 regular-cab chassis-cab f-450/550/600 with 84" CA and "aft-axle frame extensions" will have a much smaller turning radius due to the front axle and the much shorter wheelbase compare to the CCLB pickup truck.

 

[Mike W.]

It ultimately comes down to how much weight you plan on hanging over the back and if you plan on any type of towing. Also how structurally sound your build is. Less is always better as to overhang.

 

[rruff]

Use case: casual off road - bad forestry roads, washboard, drainage ditches from Baja to Yukon... We started thinking ~40' Class A but then realized that limits our places to access too severely.

It's definitely a compromise... more interior space is not necessarily merrier, since a bigger rig will be tough to take places. If hiking and kayaking in remote areas is a high priority, I wouldn't get carried away. The correct size is just big enough.

Whether you should even consider this sort of life depends on you... and more importantly your wife! It's a tremendous undertaking and expense to do a custom rig like this. Not something you'd do unless you're both pretty damn sure you'd love it.

Your sketch hangs very low on the sides and back. You'll need some sort of pivoting frame, and your floor on the center area will be about at the level of the line I drew. On the sides you can have extra storage, but don't cut into your ground clearance too much. The Earthroamer for comparison.

 

[Victorian]

It's definitely a compromise... more interior space is not necessarily merrier, since a bigger rig will be tough to take places. If hiking and kayaking in remote areas is a high priority, I wouldn't get carried away. The correct size is just big enough.

Whether you should even consider this sort of life depends on you... and more importantly your wife! It's a tremendous undertaking and expense to do a custom rig like this. Not something you'd do unless you're both pretty damn sure you'd love it.

Your sketch hangs very low on the sides and back. You'll need some sort of pivoting frame, and your floor on the center area will be about at the level of the line I drew. On the sides you can have extra storage, but don't cut into your ground clearance too much. The Earthroamer for comparison.

View attachment 765995

like this one? https://www.ddgoverland.com/

 

[rruff]

That one is even for sale from Rogue Vehicles in Bend.

 

[unreng]

Go for it!

The frame is extended about 30-inches and holds a winch and the receivers.
Find a builder who uses Total Composites and ask your questions.
I can post more photos if it helps.
The ddgoverland build looks well done (from my internet armchair).

 

[IdaSHO]

Assuming the design is conscious of weight, you should have no trouble with considerable overhang.

Even my "little" F250 is fine with essentially 48" of overhang.
The chassis was lengthened (added to the rear) 24" and the camper overhangs another 24"

I would suggest (as other have) to do exactly that, extend the chassis to properly support things.

 

[RAM5500 CAMPERTHING]

If ordering a brand new chassis to start with, if you went with a regular cab, you can order the chassis in up to CA120 which would NOT require any frame lengthening, etc...

 

[displacedtexan]

Why the back seat??

2 people, buy a regular cab... often discounted and get a longer frame to build on. 90% of the broken frames are related to excessive, even if built to spec rear overhangs.

What is the advantage of a back seat?

I'm alone 90% plus of my driving in my truck. I won't own anything but a 4 door.

Accessible storage.

Stuff happens, I've carried people off a mountain before.