Dirt and vibrations you seem to have covered. Only other thing I can think of is damage from rock strike etc? Would be a pisser if you couldn't put your tent up because summat had pinged into your poles while on the trail. Probably pretty unlikely though.
Also, an alternative to strapping them to the frame would be one of these downtube bags (need to be 50cm long and then tyre clearance might be a problem)
Dirt and vibrations you seem to have covered. Only other thing I can think of is damage from rock strike etc? Would be a pisser if you couldn't put your tent up because summat had pinged into your poles while on the trail. Probably pretty unlikely though.