I installed a 320 in my 26' FKWS flagstaff without a problem. just measure the distance you have to the rear wall to see if you have clearance, Many folks have made mods when the clearance was not there. Removing and replacing an RV toilet on the DIY scale is a one or two so very easy to do.
Jake my sidekick (yellow Lab) 10/04 - 05/20
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho