There may be 2 support structures, 14" apart, running the length of you coach. That's what Fleetwood did when they built my 95 Bounder. Get a stud finder and have a look. You could fasten to those supports if they exist.
Richard
95 Bounder 32H F53 460
2013 CRV Toad
2 Segways in Toad
First brake job
1941 Hudson