Could the bolts holding the frame be too tight, and forcing the gasket to ooze out ? Even if you trim it, it might continue to ooze out, and eventually there wouldn't be enough gasket left to make the seal.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.