Super soft rings allow you to add body-to-chassis compliance for a suspension-type effect.
Washers can be used under the head of the screws below the chassis and also between the chassis and body. The washers can be cut down with scissors if softer action is needed.
These are also applicable if the car has a separate motor pod to add a modulated adjustable suspension effect between the pod and the chassis main plate.
Washers material can take repeated compressions and expand back to original shape.