expansion of hardware

i think last time i posted on here, i only had a Dell optiplex 5090 MFF, and a GMKtex Nucbox.

i now how added to those a dell optiplex 7080 MFF, and a HP Elitedesk MFF

all 4 machines are stacked, right now but i feel i need to put a gap between each of them. i'm not sure if i should look at getting a small metal rack from amazon, build something simple out of wood to just stack and add say 12mm (half inch) between them, or 3d print something for it.

i have a 3d printer able to print in PETG, just don't have much (just a ton of PLA) but i also don't have any timber so all 3 options i'd need to go buy something to put the air gap in between.

i can see myself buying more MFF machines in the future so i'd rather not have something that isn't expandable (the metal rack from amazon for instance)

so really my question is do i "need" to put air gaps between MFF "servers" or is it more a aesthetics thing?