Do you use the motormount with one motor on the highest point?
I don't like the idea, that a motor with a 1/8th shaft can wiggle on the spur.. makes the shaft snaps easier.. cant you think of a motorbrace?
I made one like this;
It's made from 10 mm x 2 mm aluminum.
mounted, sanded and polished it looks like this;
I am sure you can find a way to connect it to the chassis..