GRIT!!! Kills Tanks,
A decent bulkhead between the gearboxes and the rest of the hull so that your regular but sparing application of Lithium grease to the gearbox bearings while keeping the gears clean and free of GRIT won't spray over the electrics.
Regular tightening of the axle grub screws, look for track pins coming adrift, and a very close look using a glass at the control board for any signs of burning which will lead to short circuits.
shaun