Use a water tight fitting to go through the roof.
https://www.amazon.com/uxcell-Waterp...rproof+Plastic
Really decide where you are going to put the battery and inverter. Its a pain to reroute wires later. Use a good inverter and battery. The cost can be high but the performance is higher. 1500 watt pure would be my minimum suggestion. You can also run a fuse block and run all your interior LED's, add a socket for a 12volt blanket, ect.
I've been running a solar unit on my son's race trailer for over a year and it has been 100% maintenance free. Love it.
In my van I run two house batteries via a VSR. It could be easily converted to solar charging.