There are a few things which I'd trust to professionals. Pouring concrete is something I'd do pretty much once, so I want to make sure the job is done right.
If I had to do it myself (since Harvey has gotten every single handiman out of the woodwork and building in Houston), I would be getting people who know something about concrete, getting some equipment to compact the soil, get the forms in place, make sure there is enough rebar present, pour ten inches (RVs are heavy), make sure the concrete is wet so it cures at max strength, and wait at least seven days, ideally 14 before my stuff goes on it.
I mention 8-10 inches because RVs are heavy relative to other vehicles, especially if someone also has a truck on the slab as well.
There are other issues as well. Drainage comes to mind.