Put AC on Roof of older model 1990 M-28

I Purcheds a 1990 M-28 last summer. We found that the side mount AC does not keep up when camping in South Texas. I did a search and can not find much information about the possibility of putting a roof top airconditioner on an older trailmanor.
Did they add additional support in the newer models for the roof top AC? I know I will have to see if I can adjust the torsion bars with the added weight. Any insight if anyone has done this would be help full.