I have the linked cable entry plate. Some would say it's overkill and they're likely right, but it seemed like the right tool for the job. It's expensive. I'm very inexperienced but keep in mind that, so far as I can tell, it's not meant to be used to simply run long cables through, from the roof to the controller. The plate is meant to have MC4 connectors mounted in it, so you'd need to cut the wire and attach those. If you buy the plate with these already mounted with attached wire long enough to make it to the charge controller...even more expensive. Seems to be hard to track down lately, too.
I went with just VHB tape for my panel but if I had to do it again, I'd probably at least bolt two diagonal corners, through the ceiling. I likely will do that at some point. You'll hear from people from both camps, but in the end, there are already holes in your roof. So long as you seal them, they won't leak. I used VHB tape, covered with sealant (sikaflex, which was a mistake), covered again with eternabond tape, which adds more stability/larger footprint of adhesion. But still...crazy enough gust of wind driving at highway speeds...
I put my panel on the back end of the roof, ran the wires along the roof to the front, driver side corner, closest to the power center and battery
, then down through that corner into the cabinets, along the corner beam, down into the lower cabinets/dinette, to the charge controller which I mounted under the front dinette seat, right above where all the wires come through the floor. Close to the battery
You have the benefit of a torn-apart trailer to work with. You can add supports and anchors anywhere you want for securing things.