One alternative to the MEC Supersizer...
If you look on ebay, you can often find the old 12 gauge RCBS 12 gauge shotgun dies. I'm not talking about the version they sell now, but the version they used to sell that was made for reloading plastic and paper hulls.
You can deprime, resize, reprime with it. If you are doing BP and cardboard/fiber wads, the rest of the operations can be done with a wooden dowel. Crimping with a roll crimp can be done on a drill press or even a hand drill.
The die will resize the hull bases nicely. The only drawback is that you will need a Rockchucker or a Lee Cast Classic to hold them as they wont fit in a standard 7/8" reloading press.
I think the Supersizer goes down a little bit further towards the rim on the hull, but I am just throwing the RCBS dies out as another option. If your extractors are at least pulling the hulls out a bit when you break open the gun, it probably doesn't matter if the hulls are sized down as far as possible.
I havn't tried the RCBS "BRASS HULL COWBOY DIE" on a plastic hull,. it might work too, but it wont reprime for you (different primer sizes). I have both sets, so I never had a reason to try to use one for the other.