There are some options for you to help make the AC run cooler. Those include adding some sun deflection/insulation. Even changing the direction pointed can make a difference.
Things we've found to work include sunscreen awnings, reflective in the windows/skylights or covering the skylights. You don't have to leave them in place all day, but they can do a lot to reduce the heat in the hottest part of the day.
Assuming you are an early riser, make sure you cool off the inside as much as possible.
What size 5th wheel are we talking about and what size BTU unit? I'd be surprised if one is enough unless it's really short.
