Jeman you mentioned bracing the gearboxes,
Well the way I do it is to use a bit of Plastic channel (the Panzer 4 radio aerial storage channel is what I use)
Cut the channel into two 2cm lengths ,
The aerial storage channel slot is 1mm wide, so, glue the two pieces of channel to opposite sides of the hull immediately behind the gearboxes.
Cut a piece of 1mm thick plasti-card to size and slide it into the slots formed by the installed channel,do not forget to make a hole for the gearbox cables to pass through.
DO NOT glue the bulkhead as you will need to move it sometimes.
Job done, and it has the added advantage of keeping any lubricant from the gearboxes being thrown over the electrics.
This is a modification that works with any Tank with front mounted gearboxes.

shaun