I did not need extension wire (thought I may have but didn't need it, my MH is a 32 footer and had more than enough wire. Ran from back to the front engine compartment to mount the switch box with all wires then from switch box through firewall to the monitor. Could of ran through engine cover, but put all items under hood within easy reach for future if needed. Actually, screwed switch box to the fuse panel cover. I will try to post some pics soon of everything. Just for extra ptotection also, I covered the camera cable with the split black flexable conduit also but probably wasn't needed, ran out at engine compartment on one wire but most all is covered and will add more soon as I already bought more of the plastic conduit.
Oh, I also went to back reverse light and found colored wire for reverse bulb and found other end of same color wire at transmission and tested and spliced there instead of running wire from back reverse light to the switch box but was prepared to do that if needed. Happened to find it closer however easily, so did it towards front to simplify running wires.