Just bought a 6x12 enclosed trailer. Ordered ATK bike shoes but I still need a few tie down points. Just how do you mount d rings to these trailers? I'm thinking of getting the floor recessed and the flush wall mount type. Do you just mount using self tapping screws? To the frame of course. How hard are recessed type to mount to floor? Do you just cut a 3" hole? And mount two of the holes to frame with backing plate? You can see I'm a newbie in trailer world. Any hints and tips appreciated.