cool idea!I found doing it inside a largish (so you can stand in it - 4 man I think) dome tent works quite well... after your done you just sweep it all up and it doesn't go everywhere. Bit unconventional I know but if you are on a budget like me then you canne argue
hmmm, got any pics of that, id be interested to see this..yes, I use a 45 gallon plastic drum, the sort that you can bulk buy chemicals in, with a wooden window frame grafted in. cut two arm holes with a 4" hole cutter, wired in an ordinary 60 bulb and stuck an old vacuum cleaner (do NOT use the missus' dyson and expect to get away with it!) in one of the original barrel holes. the vacuum helps clear dust and suck your sleeves to the sides of the arm holes, it also helps keep the grit clean, taking away the less dense bits; I never have to change it, just top up every now and again. I don't tend to wear gloves, ricocheted beads are not too uncomfortable, you'll know about it if you point it directly at yourself tho!
may be a bit small for anything too big, the biggest thing I've had in there is the louvered panel below the rear window of a beetle. also, if you do do this, try to get one thats had something fairly inert in it - mine had some kind of grass additive in it and has take about a year to stop smelling of garlic
edit: a plywood box would also be fine!