In all seriousness - you're adding pounds to the weight of what is already the heaviest instrument in a marching band. Just don't bother. If you have any smaller kids or weaker freshmen, you're putting an instrument on them that will wind up weighing 40% of their body weight.
That being said, the King 2350W (preferably in silver) is my go-to sousaphone. The Conn 20k series is also good, but a bit heavier (and wider bore) I've noticed.