IMHO, you might be better off making a longer run and using a vent to get the wiring under the trailer, where you can easily follow the frame forward and then go back up into your forward storage compartment. That's how I installed mine, although I do have a smaller trailer than yours. It just seems that you might be in for a major project you didn't want by trying to go down through a wall. Not to mention making a new hole in the roof.
The voltage drop of a longer run can be mitigated by using heavier wire. Or, as 2Oldman said, you can increase the voltage (thereby making voltage drop less of an issue) by putting panels in series.
