I made some repairs in a rented storage lot. I've seen others making far more extensive repairs there than those I did.
I did one emergency repair in a church parking lot. Be especially careful not to leave messy stains from RV fluids behind. I always carry pieces of cardboard to lay on and to make it easier to slide under and out as well as newspaper to absorb minor spills. Wad them up and contain them in plastic shopping bags for disposal.
As I've pointed out elsewhere, the Pioneer camp ground in Whitehorse, Yukon (just in case someone reading this is on the trip to Alaska) has great repair facilities available where you can power wash and/or get your RV up on a rack where you can stand up under it.
Minor things like oil changes, fuel filter replacements, brake line repairs and bleeding, etc. I've done in NAPA, AutoZone and Advance Auto parking lots after buying parts there. Many of these places really do not care so long as you stay out of the way.
Lastly, I did one oil change in a municipal parking lot while my wife did laundry. I admit I was a bit stealthy about that one since I was not sure if I broke any laws. OTOH, I didn't spill a single drop of oil that was not onto my cardboard, so no lingering guilt feelings.
WalMart sells a nice oil drain pan that doubles as a container to take used oil for recycling. Big enough for gassers only.
If none of this solves your problem, it might be worthwhile to simply hire an RV service center to do the work. It feels good to simply pay the bill... no dirty hands required.