So far as how to start.... look at types/shapes of sheds. I would want one with enough extra width/length to shade the sides and ends of the RV and park another vehicle. Pour the concrete wide enough for a patio and extend the cover for shade. Add some good safe steps that aren't too steep, that you can move out of the way when you leave.
So far as tiedowns---you would want to anchor to the chassis and some sort of point embedded in the concrete, like for pool covers. Find out what local codes require.
Decide what you want and then find a good licensed general contractor to work with. They will know how to get the permitting, excavation, wiring, etc. You will probably need (and want) an inspection on the water line and septic tank. You may need to get the septic tank pumped.