I am about to buy Jim's final Viv and plan to put in on top of Rosie's. They will both be new vivexoctic viva. Would you advocate adding feet so that there is a gap for the circulation of air between them?
I've stuck mine straight on top of each other, no gap. However, if you are using ceramics as a heaters, that can cause the floor of the vivarium above the heater to become quite warm ( so I've heard, I haven't used ceramic myself ) - so you might need to consider an air gap then.