I'd run wiring for a 50 amp rig. If burying wire, PUT IN CONDUIT or some %$#$ critter will eat part of the wires making you rerun wires. Do not ask how I discovered this.
I'd also look to see how hard it was to add a dump inlet. Sure would be nice.
Be sure garage is WIDE and LONG enough that you can use a creeper all around, even after the junk starts piling up around the walls. Know someone who has to move RV out of garage to work on it. Boy is he unhappy about that.
If you plan on washing inside, not something I would do, have the foundation extend up the walls about 16" above the floor. Makes spraying floor much easier, and saves wetting sheetrock.