If an amp can't handle being rolled around on casters then it's an unreliable amp, IMHO. They used to test Traynors for durability by dropping them out of a second story window, so I'm told, anyway. Have you ever tried to vibrate apart a solder joint? Ain't happening. Now what definitely can happen is tubes can jostle loose in their sockets. But that happens just driving around and going over bumps. I always make sure all my tubes are nicely seated before firing up the amp after moving it around. All it takes is a few minutes of thinking about physics and forces to realize this is an absurd concern. If you can't pull apart a solder joint by yanking on a wire with a lot of force, then there ain't no way some minor vibrations are going to do anything.