Easy to mount to the beams in the trailer. They've been in for a year and full of gear. I don't see any evidence of them coming lose from being jostled around by road vibration. They make several sizes. I believe mine are 12"d x 18"h x 36"w. They are easier to mount with a helper, but you can do it by yourself. They sell premade utility cabinets, but the ones I'm referring to are the ones you have to assemble.
Try this link, it doesn't have all of the cabinets, but mine is basically the shorter version of the C5, only 2 doors, but I installed four of them, so each of the family gets there own cabinet for gear.
http://www.millspride.com/mills/ourproducts/stor_items_c5.htm
I found that the 30 inch cabinets were too low with my 6' ceiling, I couldn't open the doors all the way with the bikes in the trailer.