Rocket launcher ideas???

Okay, Ive been playing several airsoft scenarios that would work better with an RPG-type weapon. (I wasn't sure if there was a thread about this if there was I'm sorry). Anyways, I've thought about using a potato gun as the RPG, but does anyone else have any other ideas? My personal funds aren't quite big enough for me to buy something similar. Any suggestions are welcomed and appreciated.

Do NOT use a potatoe gun. You'll end up injuring someone.

PM durkee he's was working on an AT-4 and an RPG he has some good ideas. I think you could do a pvc tube large enough for a nerf football, then get a giant spring and a way to push the ball. figure out a trigger system and make it spring opperated.