Assuming Ride-right helper air bags or similar: I find somewhere in the vicinity of 40 psi seems to be about right for my '98 Coachmen of roughly the same length. I think 20 psi was the minimum permissible and 90 or 100 psi the maximum. You can get a bit of an idea by watching how the ride height of the vehicle changes as you put air in or take air out.
I just replaced the valve core in one of the fillers for one of my air bags the other day, as chance would have it. The old one wasn't sealing properly (though the screw-on valve cap did prevent air loss effectively, so it was more of a nuisance than an emergency). Of course, replacing valve cores is nearly as hard as replacing light bulbs, and maybe less expensive.