What if you just let some air out of the rear tires on the truck until things are level?
Nahh just kidding :O
I agree that "heavier" springs are not the way to go. You would be just adding a new problem by beating up the RV both internally and structurally.
I also agree that a spring shop is a better place to go than an RV dealer.
If you are spring under right now the srping over conversion is easy and will fix your issue without adding any new ones
As well a good spring shop can come up with a good plan that is both feasible and sound.