Properly designed rack gear is designed to be held by the rack ears, or comes with provisions for rear support if rear support is really needed. Just keep the screws tight. It's good enough for nuclear power plant controls... For transport, face up does mitigate the effects of bumps on the road, etc. The rear-mounted tray is a nice belt and suspenders option so long as it does not block any vents; (belt and braces for members of the commonwealth who are now snickering.)
Ventilation counts - depends on how the amp is vented - if heat blows out the back, it doesn't really matter where it is, if air flows bottom to top, it does, and cooking other parts of the rig above it is an issue. The rack shown is nowhere near tall enough for stability to be a major concern from putting the amp's weight on top. If it vents up, dropping everything one space might make sense (with or without a cute perforated fill in panel) for better ventilation.
Ventilation counts - depends on how the amp is vented - if heat blows out the back, it doesn't really matter where it is, if air flows bottom to top, it does, and cooking other parts of the rig above it is an issue. The rack shown is nowhere near tall enough for stability to be a major concern from putting the amp's weight on top. If it vents up, dropping everything one space might make sense (with or without a cute perforated fill in panel) for better ventilation.
