Here's my solution for a prototyping chassis.
The H-frame is borrowed from an antique transistor tester chassis (what is a transistor, Mommy...). Even the tallest tubes, placed on the middle deck, are within the H-profile, so it can be rolled on any side safely.
Instead of drilling all sorts of socket holes on the steel deck, I use disposable top boards made of laminated floor chipboard. Here's a Mullard EL84 prototype. If space becomes too clogged, heavy parts can be bolted to side frames.