On my previous TT, I used 1 X 3 stand-offs around the edges, then every 20" o.c., and used pegboard. The pegboard hardware came with plastic clips that bridged from hole to hole, and held the hardware in place.
Be Safe, and Everyone Goes a Home,
2014 RAM Laramie 2500 w/6.7L Cummins Diesel and Automated Safety Hitch
2016 377RLBH Jayco North Point
300W of Suntech Solar w/Rogue MPPT Controller & Xantrex 2000W PSW Inverter