I went with small "L" brackets evenly spaced to mount/attach to the sides of the 215 watt panel and to the roof of the camper. Used screws/washers and my friend Dicor self-leveling. Just screws and washers and Dicor for the flexible panels.
2012 FunFinder X 210UDS
4-68 watt flexible panels; 1-215 glass panel/4 Battle Born LiFePO4 Deep Cycle Batteries
2014 Ford F350 6.7 Liter PowerStroke V-8 Diesel longbed, SRW