@ Munter - will make a shallow driver tray from .015 sheet styrene and mount a driver figure from the Fujimi Drivers kit that I just picked up at a recent model swap meet.
Started on a dedicated chassis.

This one's more piano wire than the Tiger's. Main rails and front axle uprights are .055" wire with guide tongue and rear crossmember made from .032"x .75" brass sheet. Motor mount's the JK off set one, .75" wide.
Spent some time getting it "flat and square" as emphasized by Chrisguyw. All four wheels/tires sit solidly on the surface at the same time.
Wheels are Mitoos five-spoke 17.5 x 10 and 19 x 10.5 rims, front and rear, with Scale Auto 24 x 10 tires all around.
Dan