In
this thread I mentioned the use of a linear actuator that we have successfully retrofitted with a bag motor with relative ease. Put a flat on the motor shaft and drill 2 new mounting holes for the motor and voila. The mentioned actuator can be found below. It is rated for 200 lbs of static load (could probably go a little higher) and there are stronger models available. Also it is fairly cheap. Sub $100.
http://www.princessauto.com/en/detai...or/A-p8489098e