put em on bricks/concrete blocks. buy quality gear. I used metal tool boxes once. was great they opened easily if repair needed. no tool required open latch
I have my ballasts in an sheetmetal pan and it has a tall back on it for the wall....the sit there stacked on top of one another and have a fan blowing on them. I vacuum these with a shop vac weekly to keep dirt down on the ballast cooling holes of which I also drilled them out larger.
I have had my mag ballasts for over 15 years and my digi's for over 5 and all run great without a hitch.