I say yes on camp permission to do necessary safety driveline work when the unit cannot be driven safely for repairs., , no on routine maintenance like an oil change. Thats work for a shop with knowledgeable mechanics and capacity to deal with used fluids.
Engine & Tranny oil pans are stamped sheet metal, can easily be deformed by incorrect torque pattern during removal and reinstallation.
I disagree with another posters comment that suggests you write reviews reflecting on the camp. Even if the camp authorized, recommended the service provider, they have no knowledge that this one mechanic did not perform as well as others. Tell the camp hes no good, take him off their list of service providers.
Review the repair company, do not disparage the camp. Looks to me the camp was willing to work with you in every way, and you with them by doing everything to contain possible spills.
Do your service before or after camping. Not in camp.