Almost finished my build, need help finishing up

If you get any truck frame flex, that will be transfer into forces on your camper frame if directly bolted together. Although it is done, I would rather see a spring load device between the camper and truck for that reason.

If you could slide the camper farther forward so you have minimal overhang, then you would not need a hitch extension. This would allow you to use the existing receiver but you will need to find an alternate location for your auxiliary fuel tank.