This is a mount I printed for my mother's RV. It has been working well for her for about a month now.

It's meant to be mounted with six 1" gasketed sheet metal screws. I put down butyl tape to seal it, but considered silicone calk as well. It requires a 1/4" threaded rod for each channel to hold everything together securely (each is approximately 15" long). I used locking nuts on both sides with an additional nut on one side to allow me to tighten the locking nuts in place. The channels were printed vertically for strength using a 0.8mm nozzle. I printed it in ASA for UV resistance, as it is installed on the roof. For adhesion it was printed with a pretty large brim.