Popup camper frames and axles are barely adequate for the job they're designed to do, your typical "normal" size popup will have a 2000lb axle rating, larger might have 3500lb,
the frames are typically light gauge stamped C channel, using the wooden structure of the box for rigidity and strength. None of which will do well in a rugged off-road environment in stock form.
I have a large popup myself, it's own weight carrying capacity is barely adequate for itself, I've up-sized the tires to handle the load, next step (maybe) is to go too a heavier axle and a bit of lift to clear yet larger tires, 16" wheels and tires matching my towing junk would be ideal, but that brings other modifications to be made.
I think you'll find that trying to modify an existing camper may be more trouble and expense than it's worth.