Get the smallest roof AC unit u can get, I think this will be a 9200BTU, not the standard 13,500 BTU that most have. 9200 is plenty for a TC your size. The Dometic have the Polar cub that is also low profile (not as tall) so gives you a little more clearance. Bonus is that a 9200 will run off a 2000 watt generator where a 13.5 will not.
IF you can and are willing to put in a window unit then consider that option. $99 is a lot better price than $999.
This is hard to do on a TC.
A 5,000BTU should be plenty in this case.
I had a 9200 on a TC and it cooled instantly, and was over-kill to be honest.
AC roof units are sold as the roof part and the inside ceiling assembly is sold separately (usually). Sometimes you can find a rebuilt (like new) unit on eBay much cheaper. Sometimes you can find a used one for 200-300 bucks.