Sir, I used to own a 38 foot Keystone Raptor with the 5kw onan, and can tell you, it NEVER handled the air conditioning well. I mean, it worked, but I don't believe even the 5k genset could produce the current flow the AC unit required, and it really struggled to cool the coach. They are not very well insulated. When I plugged into the 50 amp shore power, I noticed an immediate difference. If you go with a smaller air conditioner, you're sizing the air to the genset rather than what the coach actually needs. I'd say you're better off going to more power as some of these guys suggested.