Trailer Frame Tube vs C-Chanel

[Strider]

I am in the planning stages of my trailer build. This will be an enclosed small camper trailer to be towed over off road behind my 2008 FJ Cruiser and maybe my wife's 2009 Jeep Unlimited Sahara. I want to make it strong but light with most of the weight at the chassis level. I live in AZ but am still concerned with tubing being prone to rust from the inside.

Considering the following for the frame:

1. 2x4x1/8 steel tube welded shut with aircraft oil inside as used in airplane frames.

2. 2x4x 1/8 steel tube with drain hole cut and painted on inside.

3. 2x4x 1/8 steel tube welded shut then paint poured in and sloshed around. Hole covered with bolt or silicone.

4. 4 or 5 inch c-channel.

Will be welding with a 110 volt wire welder/mig.

Any suggestions, advice, or warnings will be appreciated.
Thank you!

 

[highlandercj-7]

I have a 2"x3" 3/16" wall frame under my CJ trailer. I built it in 2000, and it's been in the rust belt every since. It's still like new with only paint on the exterior. You will be OK no matter what you use in AZ. IMHO tube is stronger and looks cleaner.

 

[Strider]

Sounds good

 

[java]

Tube will be stronger and possibly lighter depending on the thickness of the C. Unless its a huge trailer 2x4 is overkill IMO. I wanted super light on mine and its 2x2 .065 and .095 wall.

 

[Capt Eddie]

Different parts of the trailer should be made of different material based on the structural strength needed in each application. The tongue itself should be C channel. Structural areas may be angle or square. As a whole you would not want any more closed area then necessary. These are areas that can hold water and vermin. Look at some commercially made trailers. They are built the way they are for a reason. I do not think you will find much square tubing on high production builds. There is to much liability for tubing failure.

 

[Strider]

Tube will be stronger and possibly lighter depending on the thickness of the C. Unless its a huge trailer 2x4 is overkill IMO. I wanted super light on mine and its 2x2 .065 and .095 wall.

Trailer is going to be about 12 feet long overall with the "box" about 8 feet long x 5 feet high x just over 6 feet wide. I am seriously considering Nidacore for the skin to keep it ultra light. I am worried that the stresses off road will overcome 2x2. But I'm still figuring it out.

 

[Strider]

Different parts of the trailer should be made of different material based on the structural strength needed in each application. The tongue itself should be C channel. Structural areas may be angle or square. As a whole you would not want any more closed area then necessary. These are areas that can hold water and vermin. Look at some commercially made trailers. They are built the way they are for a reason. I do not think you will find much square tubing on high production builds. There is to much liability for tubing failure.

If I use 2x4 tubing I plan to either weld all openings shut, or maybe drill some holes to let humidity in/out and paint the inside heavily.
Why should the tongue be c-channel? Isn't c-channel weaker than tube? Or is it because of the possible rust issue?

 

[SoCal Tom]

This is a link to some EU trailer tongue specs. http://www.angib.pwp.blueyonder.co.uk/teardrop/tear61.htm They are a good guide for the strength of various metal designs. FWIW, my tear drop is made of 3/16 angle, except the tongue which is 3/16 3 inch tube. It was designed to carry 3500 lbs, however the Tear drop itself weighs about 900.
Tom

 

[Strider]

So I drew up a plan for the trailer and frame. Obviously this is a simple plan mainly for determining quantities of material and pricing.

I originally considered building all of the trailer frame using c-channel, but read repeatedly that c-channel is much weaker than tubing and that tubing is fine.

Here is the plan:



Trailer is going to be about 12 feet long overall with the "box" about 8 feet long x 5 feet high x just over 6 feet wide. I am seriously considering Nidacore for the skin to keep it ultra light. I am worried that the stresses off road will overcome 2x2. But I'm still figuring it out.
PS
Trailer is inspired by the Aussie UEV-440 and the T-Van, so I will be putting a pull out kitchen, etc. Don't know what it will weigh yet but am trying to keep it as light as possible with most of the weight at the frame level.
PPS
THANK YOU ALL for the great information so far!

 

[Strider]

So maybe I will make the whole frame out of 4 or 5 inch c-channel. Seems like 4" will be quite strong.
Is a cross member every 18" overkill?

 

[Capt Eddie]

Tubing is unidirectional, where as C channel has strength in one direction. Allowing the metal to be thicker and weld stronger. The tubing is thinner walled all the way around and the welded areas are weaker. Your strength on the tongue is 90% downward. That is where the strength of the C channel lies. The side to side strength is minimal based on the triangular principle of the tongues shape. Look at the metal as pounds per foot. A C channel the same weight as tubing has more metal on one side allowing that side to be welded correctly. 2 inch C will weld stronger in all applications then the tubing you have shown. What weld would be stronger. 4 sides of .065 or two sides of 1/8 inch? The .065 will weld and the weld is strong, but the metal will fatigue along time before the 1/8 will. The twisting of the frame would definitely tell me to use the C channel on all of the frame. As well as the rust issue. BTW. This is what I do for a living.

 

[Strider]

Capt Eddie,
Thank you very much for that information-it makes sense indeed.
I will go with 4" C all around then.
Do you think its overkill to place cross members every 18" on the frame?

 

[Capt Eddie]

If you are concerned about weight. I would not use 4" C. You had planned on a 2" Tubing. Just use a 2" C In its place. The wall thickness is twice that of the tubing. Making the welds stronger. The cross members spacing is based on the flooring material. 3/4 inch plywood, you could go 24'. 1/2 plywood will need 18". !/2 plywood,3/4 insulation then 1/2 plywood. Would be my choice. Use treated plywood on the bottom. I would use treated wood along the bottom everywhere. The condensation will still roll down the inside of the walls. Making all the wood wet. You will not notice the wood being wet. But after time the base plate of the walls and floor will start to rot. I see this on campers all the time. Syphon action keeps the water under the baseplate. Use 2 1/2 self tapping trailer screws to anchor that all down. It will tap the 1/8" C channel. Use exterior liquid nail on all pieces.

 

[Strider]

Thank you. Makes sense.
I was planning on 2x4 inch tubing with 1/8 wall for the frame and 4"C for the tongue.
The trailer will be a camper about the size of a UEV440 using fiberglass/foam walls or something like Nidacore to keep the weight down. Trying to keep the weight low. Nidacore is something like $260+ for a 1/2" 4x8 sheet + shipping and they have to cut it in half. Doing the fiberglass foam panels myself may be expensive too including time. Maybe I should starts a thread for the trailer in general.
2" C seems a little thin for this no?
A local builder quoted me $900+ to build the frame w axle. I am doing the math to see if its worth building.
Thanks again!

 

[highlandercj-7]

I'd use tube, a trailer of that size I'd go 2"x3" 3/16". My 30' Jayco uses 2"x6" tube on the frame and the tongue and weighs in at 7500 lbs. Our 44' enclosed race trailer with living quarters is also tubed, including the gooseneck and it has triple 8 lug axles. This is why trucks have evolved from C frames to boxed frames too.