Actually kind of shocking they even produced a unit that big with 1 air con. Around 28-30ft, you are reaching the limit for a single unit.
I assume the rig is a 50 amp rig (just the current site is 30amp) and it's wired up for a second air/con. Bite the bullet and get the second unit. I'll bet you every time it gets up in the low to mid 80's, it will struggle to keep the inside cool with only 1 unit.
One temporary thing, you can try is if the aircon vents close off, shut down the bedroom and bathroom and close them off so all the cool air is going to the main living area during the day. Usually at night, you don't need as much cooling, so you can open them back up.