I've never used bubble bags, actually I'm not really certain how they work. I think the ice is to cool the trichs down so they're more solid and are damaged less in the process plus it makes them less sticky. Then its filtered further and further until you get the pure trichomes which gives you that beautiful blonde hash. What I do is just the bare necessity. I screen trim through a nylon coffee filter for automatic coffee makers, then through another smaller mesh copper screen (I think metal screens are bad for some reason) and then I put it in some parchment paper(used for baking), then I warm it with a blow dryer (while its still in the paper) and then press it between books or what ever. Very little expense or effort and it actually makes a pretty decent product. That being said these folks are much more experienced than I am.http://forum.thenook.org/index.php?showtopic=28354 at the end of the thread millet talks about rebuilding a tumbler, you might check into that.
Good luck
NH