I put the pump on the seat tube this evening. So far my conclusion is that there is too much interference with my leg on the side it is on. However, I only test rode with steel toe boots and jeans so I need to to a ride set up to ride and give it a better evaluation.
The kit came with rubber "insulators" that have a nub that sticks in to the bolt holes in the bracket that are for use if you use zip ties to attach it. If the zip ties are tight enough the rubber should hold the mount in position well enough I would imagine. We'll see.
I did bolt my old pump + CO2 cartridges back on under the down tube where it was before. I figured it wouldn't hurt, I know how that one works and if things are really sour on a trek and I don't feel like pumping I can throw a CO2 cartridge in and maybe get to riding pressure without pumping, at least the bulk of it. Though, I admit - I have never used a CO2 cartridge to inflate a tire so I am not too confident in the theory.