You might get away with liquid nails or a 2 part epoxy. Hard part is the torque put on them when cranking down on a crimp or hold. Depending on where you mount them you could possibly pop a couple holes for each and back with metal plates and then bolt them on. Wouldn't be too hard to seal the holes/bolts with silicone to waterproof. Just really depends on the structure of your rig in the places you want to mount to. There is also mounting some 1x6 boards that could mount the holds to, then it would be modular.