Our rig is 38' long, one AC in the bedroom, one in the garage. It gets nice real quick when both are on, but it gets miserable real quick if the bedroom one doesn't work as there isn't a great way to get air flowing back there since the windows are small. We learned this the hard way on a boondocking trip last summer, the front AC stopped working on day 2. It usually cooled off enough when it was bedtime, but we ended up lowering the happijac bed in the back to be able to take naps during the day (which is a favorite camping past time of ours haha).