Your motorhome is stored in an enclosed building. I see your first problem being ventilation, the other being cleanliness of the air. The paint is not something you want to be inhaling, and any dust will ruin your job immediately. Doing it outside is just asking for trouble, for the same reason - one gust of wind and you're screwed by any dust kicked up.
I have no experience painting, except some work I did in a motorcycle detailing and customizing class I took in college. One minor flaw will stick out like an obvious sore thumb once the paint is on and make you wish you had paid a pro to do it in the first place. There is a lot of work involved to have something go wrong and have to re-do it. If it were me, even having one of the best painters in Ottawa having showed me the ropes, I'd fork over the $ to him to make sure it's done right in the first place.