I'll soon be setting up a rack system in a Gator 4U case. It'll be a 2U Mesa power amp that has a fan and a 1U preamp (the preamp is about half the length, front to back, of the power amp). Neither have cooling vents on the top or bottom. Should I leave one screw hole worth of space above and below each unit, or would it be fine to stack them tight and use the extra 1U for a power conditioner? I know the studio I play at has pretty good power bars (good enough that they plug their ENGLs and Mesas into them) so I don't think the conditioner is a necessity. My main concern is longevity of the units and avoiding anything that would cause the internal components to get damaged over time (e.g. too much heat).