"Hmm... I think I'll have to consider PVC... or ABS for myself as a means to build a custom pump mount for my bike. Come to think of it, has anyone built a rack out of PVC or ABS pipe? (I would imagine that ABS would work better in the case of a full rack, just because it should be stronger overall...)"

I didnt do it out of pipe, but did it out of wood and a cutting board. My custom commuter trunk that comes off incredibly easily is sitting on top. Although it does sway a small amount it has worked just fine for about a year.
http://i2.photobucket.com/albums/y23...trunk4_6_1.jpg
Scott