I am not a fan of slipping wire leads under screw down lugs.
Whenever possible I always go for the crimp-on ring terminals and use adhesive type heat shrink ends to cover the terminals. Especially if being outside in the weather.
All of my cable are usually ANCOR Marine Brand wiring and all of my connections are BLUE SEA Products (Fuse bars, Bus Bar, Switches, etc) that uses RING TERMINAL connections...
I am a big fan of using PVC electrical conduit boxes and PVC FLEXIBLE Conduit running wires from point A to B. Not a fan of just running cables laying loose everywhere.
This type of PVC Electrical Junction Box can be drilled through the center of it to go through Walls etc keeping all of the outside wiring enclosed. These boxes come in all sizes and number of ports... These boxes have weather tights lids... Even my WIRE BUSS connections will be done inside one of these weather tight boxes. All available from LOWE.


On the roof areas I would probably use solid PVC Conduit and Flexible type PVC Conduit inside the trailer. You also have to consider what UV's will do to your outside PVC items as well...
My solar panel wiring will also have molded weather tight quick disconnects so the panels may be easily removed.
This is the way we did similar projects in my working years with SPAWAR Charlestion NAVY Shore Facility Electronic Installations...
Roy Ken