Can you explain the rear axle rating? MY GAWR is 3800 in the rear, so can't imagine a 1000lb camper is that big of a deal. A not sure why a 5.5 box makes a difference if you get a shorter camper (aka not sticking way off the end of the bed), the 6.5 box doesnt have more payload. In fact the few 6.5 boxes I looked at had less payload since there is more truck overall.
1000lb camper, wife and I and dog (300lbs), 150lbs water, 100lbs gear, 50lbs food and we are just under payload.
I have a hard time with the idea that a camper meant for a midsize truck is gonna cause issues with a half ton....Sure if you get a 40K hallmark with all the bells and whistles sure. But I'm talking about something more basic.
I see what you're saying. If you get a camper that is made for a 5.5' box (none of it is hanging off the back) then you'd be OK if it's really only 1000 pounds for the camper.
I have the same GAWR as you for my truck (3800#). That's the maximum weight, including the truck itself plus all passengers and gear that the rear axle is designed for (I'm sure it's designed with a factor of safety, but per the specs, that's the max weight that should be over the rear axle).
The truck itself weighs about 5500#. More than half of that is taken up by the front axle because that's where the engine is located. Let's say it's 65% over the front axle and 35% over the rear axle. That's almost 2000 pounds you already have over the rear axle. So you have about 1800 pounds left to work with. The camper is only 1000 pounds, but that's empty, dry weight. Once you add in water, gear, passengers, etc. it starts to add up quickly. The weight of the camper would be almost completely over the rear axle, but the passengers and gear (if it's inside the truck) will be spread out between the two.
I only point this out because, for F150s, if you're getting close to the payload limit you're also starting to get close to the rear GAWR, which is not ideal. Other trucks have higher axle ratings so that when you're at max payload you still have some room to work with on the axles.
Anyway you'll be fine with a 1000# camper built for a 5.5' bed. Where you are you seeing these? Is that the FWC Raven model? If so, I think you'd be fine with a FWC Raven that is build as the "shell only" plus a heater. But when you start looking at a "full camper" that include the kitchen, dinette seating, etc. that's probably going to end up over 1000 pounds, even for the 5.5' Raven model.
I just went to the FWC website and they show the Raven as being 1050# for the "full camper". But when you start building it out and selecting add-ons (i.e batteries, etc.), you end up closer to 1400 # (at least that's where I was when I was building out the one I wanted). And keep in mind that camper manufacturers are notorious for lowballing camper weights. If it ends up being closer to 1400 #, and your payload is only 1700# then you're right at payload as soon as you add you and your wife (no gear, food, water).
The Project M looks promising too!