Reflectix over the windows helps a lot for the level of effort and cost. The three bedroom windows in my coach pretty much stay covered year round unless the view is something worth looking at. Ceiling vents and shower skylight are also covered with Reflectix. A solar screen for the windshield will help a lot over the interior curtin.
I normally run the bedroom A/C as cold as it will go and use a box fan to push the air forward while the front A/C set to higher temp and cycles as needed. Night time we swap back to front. Moves the noise of the blowers. The only change I make between parked and moving is the windshield screen. Over night I try and cool down the coach as much as possible, within limits of comfort, to gain on the heat of the day.
Clean the air filters, the blowers and the heat exchanger fins both in the condenser (the one that gets hot) and the evaporator (the one that gets cold) will go along way to improving the limited efficient of the unit. If the fins on the heat exchanges are bent or damaged do your best to straighten them back to original position. Check the ducting where you can see or touch it. Air leaks or loose fitting duct work will reduce the system capacity. Seal where you can. Treat the coach the same as you homestead as far as improving efficient of the system. Clean and seal where possible.