Hey Joe, I picked up some longer cables at West Marine, they have heavy gauge wire that is nice and flexible. I am pretty sure they have a way to splice the wires together, or you could get one of those heavy 2 prong connectors, the type they use on forklifts, warn also sells them for there receiver mount winches. That way you can use that point to hook up a pair of jumper cables using the same type of connector and not have to go into the seat compartment.
As far as running the cables, I ran them next to the frame all the way to the T-case mount, from there I ran then up into the seat box and connected them directly to the battery.
Don't forget to Search first then ask questions later! The loose nut behind the wheel