Scott. I don't know if your interested or not but this is what I'm going to use on future excavator build
It's a four channel remote used for door locks and trunks for full sized autos.
There are four latching relays that will give you tracks forward and reverse both sides and you wouldn't to run wires to the car body. It says 12 volts and I just tried it and it works on 7.2 if you need to. Card size is 4 1/2 x 3x 3/4 thick. I bought them up here for $20.00 a unit.
Rob