From doing our own small, 24' coach twice a year I would tell you to say thanks but no thanks to anyone who ask for a rv detail, no market would tolerate what you would have to charge to make even half your regular rate.
These are the pitfalls (hopefully you won't!, fall that is) height, roof construction and the fact that almost all spend their entire lives outdoors.
I think that the biggest time eater is doing the roof. Even with staging and planking I can spend a full 5 hours doing our roof and it is dimpled fiberglass as compared to an epdm or rubber roof. With ours it only requires the same products that are used on the sidewall, rubber roofs need additional cleaners and protectants and a lot of additional time. With our previous rv, rubber roof, a full day was needed to brush clean and treat the roof.
Most importantly you need to realize that rv construction practices are horrific at best and the roof is usually the worst of the worst-I would never walk without plywood covered with carpeting on ANY rv, even if the roof is represented as being 'fully walkable'. Many times I have heard of people ripping the rubber membrane simply by walking on the roof and turning-the membrane is paper thin and if you don't get quickly into the habit of lifting your feet before you turn, the odds are that you will at least separate the membrane from the luan underneath, or more likely, that on older units, you will rip the rubber.
You MUST be certain that your insurance covers this type of vehicle AND your working well off the ground-I guarantee you that you will hear; "but we never had any roof leaks BEFORE you walked all over the top".
But it gets better; some sidewalls are painted fiberglass, and some are painted gel coat fiberglass-different stuff requiring different stuff..
Like I said I have a small coach, only 9'8" off the ground and it takes me a full day and a half to wash, clay, wash, and use the Twins- x's 3 on the roof and x's 2 on the rest of the coach.
I suppose you may find someone who is willing to pay a fair price, but I doubt it- PLUS rv people are alot like private aircraft folk-as the length gets longer (or the knots get higher) the attitude increases at a factor of 10.
Hope this helps.