Marbles, nuts and bolts etc. and your choice of liquid. Cheap? Yeah, diesel might work. Put your tailgate down strap the tank to it and find your bumpiest dirt road. That'll slosh it, lol. Easier too.
You know what would be awesome and I may just have the thing to rig it up. Make vibrating platform and strap it to the platform and turn it on. Leave it for about 24 rinse and repeat.
My idea take a fan motor or a grinder motor weld a counter weight to the shaft mount it on a piece of wood attached to a sheet of plywood with some old valve springs or something that will let it vibrate and move. Might work? I think in missed my calling as an engineer! Haha
