Strap to roof rack, LP compartment in place of one of the bottles, find a better can to strap to the ladder, hitch rack behind the bumper, rotopax can mounted to ladder or make a mount on the back wall. All possibilities depending on camper configuration.
Also Mountain Addiction makes quality fuel jugs and racks for them that don’t vent and don’t leak at all. (I carry fuel strapped to my snomachines over far tougher terrain covered in snow and ice and water with no issue for years with these). They are kinda spendy though.