What about using bumbleballs? Battery operated, just turn them on and throw them into your body bag and they'll bounce around in there all night. You might want to tether them to something (i.e. brick) to keep them at one end of the bag though.I am going to expand my lab room this year.
Last year it was too lame. It didnt scare anyone.
I used the Doctor Shivers prop and had a pneumatic bloody body that I built which pops up using a motion detector. You can see my lab room at youtube at about 1:50 YouTube - Chestnut Hill Haunted House 08 Vid 2.
This year I will be dropping the Doctor Shivers. I think it is kinda of dumb. I will have a bloody curtain with a real person that pops out.
Behind the bloody sit up guy, I want to have two kicking body bags. I dont want to build it with air because I have another prop that I am building now that is air. I want to use wiper motors or something to make the body bags kick around violently. Any ideas?