Totally agree with this! The metal vertical studs are relatively sturdy, but are certainly not intended to support vertical E-Track. They have no reinforcing struts and are usually only attached to the inner and outer skin except for at the top and the bottom. Mounting E-Track horizontally effectively "ties" struts together and is far less likely to over-stress the struts. Using self tapping hex head screws with two per strut on horizontal E-Track makes for a pretty solid mounting platform. It's rare that anything longer than 3/4" screws will be appropriate, but you can determine length yourself by backing out the screws along one seam, pulling the interior skin away from the strut, and just measuring depth. Also remember that self tapping screws do not mean self DRILLING screws. Two cordless drivers/drills make this process very easy. One with a small bit for the pilot hole, and one with a socket driver to put the self tapping screw in. Finally, make sure you work from one end to the other when putting the screws in. Both the E-Track and the wall of that trailer can flex..... You don't want a bow in your trailer wall.
Grab a roll of painters tape, and walk around "configuring" your trailer by using the tape on walls and floors marking the position of how you'd optimally like it laid out. Then use horizontal E-Track where appropriate, as well as E-Track on the floor. When you're done, walk away from it for a bit, then come back and review. You'll almost certainly find that you can use more E-Track mounting points than you initially pick out.
If you have a second set of hands to help hold E-Track sections, you'll find it goes EXTREMELY fast. The hard part is figuring out where you want it to go. Once that is done, actually mounting E-Track is really fast. It usually takes me no more than an hour to do a 24 foot or 30 foot trailer. And every time I've done a trailer for either myself or somebody else, later we decide we could have done it a little better in terms of layout. Just the nature of the beast.
Probably not a good idea. Usually the studs are pretty narrow such that you would only be using holes on one side of the etrack to mount. The only way I think it would work is if you lined your interior walls with thicker plywood and then mounted the etrack to that.
Usually just mounting a high and low horizontal etrack is enough for almost any combination that you need.
Last tip, self tapping sheet metal screws are great for mounting to trailer studs, but make sure you get ones that aren't long enough to poke through your trailer and out through the exterior sheet metal.
