I've found "Molly" style expansion anchors to be very effective in thin paneling. The wide spread legs provide far more holding power than a pop rivet can in that situation. Toggle bolts also work pretty well, but are more problematic if future removal and re-installation might be needed.
Dutch
2001 GBM Landau 34' Class A
F53 chassis, Triton V10, TST TPMS
Bigfoot Automatic Leveling System
2011 Toyota RAV4 4WD/Remco pump
ReadyBrute Elite tow bar/Blue Ox baseplate