Yeah, it happens occasionally. Only way to fix it properly is find a frame guy who's done the repair before. The bottom skin and maybe some side skin (not always) has to be pulled back to allow for a welded reinforcement. If it's a Lippert frame, I've heard they have a guy traveling and doing repairs. Perhaps you should contact them if its theirs.
--2005 F350 Superduty Crewcab, 6.0, 4wd, short bed, 3.73 gears
--2016 Montana 3711FL, 40'
--SOLD 2014 Wildcat 327CK, 38'