Ian,
I don't know how big your vacuum motor is but of all the vacuums that i have come accross, i don't think that i have seen one suitable for the task at hand. having an electrical vacuum motor under that kind of stress is bound to bring up some problems. even if the motor is going to be strong enough in theory, it is definitly going to overheat rapidly. I definitly reccomend a blower for this. a gas motor is much better under pressure and less likely to overheat. it is also better becauseit doesn't need a vacuum chamber. i don't know what type of vacuum u would use, but if it is a shop vac than you would have to strap that whole vac to the deck. the gas is ideal if you are going to be riding on it.
If you are looking for a material for the skirt itself, it is best to use a tightly woven tarp (a few layers thick) and a rubber tubing on the bottom to be in contact with the ground on the edges.
P.S- Any vehicle that is ride on and self propelled is illegal in NY state (even if it has an
excellent driver
)