Glad you have brake experience. Chock both front wheels both ways, loosen the lug nuts then jack and block it up or use jack stands. Look for traces of heat damage from dragging the brakes in parking mode. In addition to heat damage to drum and pads, the springs could have lost tension and the cylinders could be leaky or stuck.
We bought a Class C that was on an older E350. Didn't seem the rear brakes were doing much, a lot like Ron described above. Had to pull the axles. When we got in, it was clear that it'd had a full rear brake job, at least new shoes and drums re-surfaced. Lathe marks were STILL on the drum surfaces!!! The wheel cylinders had stuck so hard, the brakes couldn't apply, hadn't worked for years.
You could make a major improvement in this RV's brakes...