Expanding on TXiceman's reply, you can't increase the wheel diameter too much or the tires won't fit in the wheel wells. Nor do you necessarily have to increase it a lot. Furthermore, wheel width is a factor too.
Instead of arbitrarily saying "LR G" and some bigger wheel diameter, figure out how much load (weight) each tire needs to carry and add some amount of extra reserve capacity to make you comfortable with it. Then look at tire sizes and load range that get you there. It's possible a larger tire alone, some combination of diameter and width, will yield the amount you need. Or maybe the size you now have, increased to LR G so it can be inflated to a higher psi. Or some combination of those.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC