If you use the typical Z brackets to secure the panels to the roof, be aware that the Z brackets add 1" to 1.5" to the "footprint" of the panel. You don't want to get too close to the edge of the roof with the panel brackets.
Unistrut is a popular alternative way to secure the panels. It's my understanding that the brackets inserted into the Unistrut should attach to the long ends of the panels, two per side. In your case, if you laid the Unistrut rails parallel to the trailer length that would work. However, if you do that then should you decide later to use a wider (not longer) panel, the rails would not be in the right position. The "solution" to that is to add another layer of Unistrut perpendicular to the existing Unistrut, which would allow you to accommodate a wider or narrower panel.
I used Z brackets to install my panels. It was only two 320 watt panels, so not a big deal. Next time, I'll probably use Unistrut. The really nice thing about the Unistrut is that you can get it secured into every roof truss. Securing anything into just the roof subsurface (OSB/plywood/etc) isn't good enough. If you have a fiberglass or aluminum roof, adhesive can be good enough (no screws), but I'm not a fan of using just adhesive.
Depending on how you plan to configure the panels (series/parallel), odd numbers of panels don't work well. If you're going to created distinct strings associated with their own solar charge controller, then the number of panels on each string doesn't matter. Attempting to parallel strings with different numbers of series panels is not optimal.
10 panels could be more than 300 lbs of additional weight on the roof, not including mounting hardware and cabling. Something to keep in mind.