To stack or not to stack - limited space for amps

I want to bi-amp with two class D SS amps. Space (shelving) is limited. I assume that it is not advisable to stack amps. However, with the amps being class D, the heat factor shouldn't be much of an issue. I was more concerned with other negative aspects?? I was considering placing one on top of the other with some form of after-market damping control (i.e.: "feet"). How bad of an idea is this? If it is doable, what type of damping product would be best utilized.

Thanks.