Many people raise their campers by "flipping the axles" to get the height they need. I've considered doing it myself but my trailer is high enough as it is. I did lower my pickup a little bit and that helped kinda split the baby and I left it alone after that.
I think you should be much more concerned that the manufacturer's claims of "1/2 ton tow-able" are nonsense and that you likely lack sufficient payload to pull any 5th wheel that big with your truck, especially if it has a 4 door cab, 4wd, and you plan on having passengers in the cab with you.
Larger rims are not going to raise the trailer at all unless they are combined with taller tires. Taller tires will likely not fit because the axle spacing is such that the taller tires will be too close to each other and could even touch when the suspension cycles. If taller tires were the solution, people wouldn't be making drastic suspension modifications to get the height they need.