Not sure why drilling/screws is a concern. I’ve worked on four horse trailers adding Rubber Maid closet shelving to the tack rooms which I’ve found to be the most versatile storage unit, readily available, and cheaper than the specific to horse trailer/barns similar systems. I am an older (ok, old) woman who rides. I have a standard cordless drill. I bought a drill bit specific for metal and the size of screws I used, and use zinc screws to avoid corrosion. It takes about an hour to install a complete 3 section “closet” unit, once you decide where you want things. Should I make a mistake (and I have) and want to move a support, I leave the screws in the holes and touch the ends with white paint so they don’t show. By inserting the shelves upside down, there is a “lip” on the edge that keeps stuff from sliding off. Further, I use bungee cords to a fasten first aid kit and brush boxes to the shelves. Oh, and my latest “discovery” is heavy duty Velcro --wrap it around broom handle, fork handle, or other tools that normally rest against a wall, place a strip on the wall of the trailer, and your tools don’t slide around or fall over! (I know that’s not what you were asking, but thought I’d throw it in.) I attached my fire extinguisher with the Velcro too, right beside the door along with the trash can.
And since I just finished my latest trailer dressing room, I do have a picture! This trailer is a bit tricky because of the curved “nose” but I made it work. I think if I were terribly clever, I could actually curve the shelves by cutting them --but not sure it would be as convenient to change them around when I show vs hunt. First photo is shelves against window/nose of trailer; second (look up) is shelving and hooks over head. FYI I put a small rug on the wall (using screws to hold it) so bridles wouldn’t bang the wall. If I were a horse, that would make me crazy!
http://i236.photobucket.com/albums/ff31/foxgloveweeks/P9130019_zpsobznwpxj.jpg
http://i236.photobucket.com/albums/ff31/foxgloveweeks/P9130017_zpsqp0ktfoy.jpg