One thing to watch for if you find the opening is prewired. If you have a 50A RV, there is the possibility it's prewired to install a second AC. If so, make sure you're getting a 12V wire and not a 110V wire. Our old RV had a secondary thermostat in the bedroom but was 30A and only came with one AC. It was set up so you could install a second AC so long as you put in the control box to run only one unit at a time. When I removed the trim, both sets of wires were there. They were clearly marked on mine, just saying be careful. I don't think that vent fan would appreciate the jolt from 110V!
2015 Legacy SR340 360RB
2014 Jeep Wrangler Unlimited Toad
Gigi, Poppy and Sadie Lady...On the road, but not full time!