this process has been a catastrophic waste of time for me, leave behind money.

i used rigidwrap plaster - because it's what's available in my area. i used four to five layers of this to make a sturdy cast, and cut it very carefully and cleanly up both sides as instructed.
nowhere on the My Twin site does it explicate what to do with adhered fabric on the inside of the plaster mold, or at least nowhere i've been able to find. i cut off any excess where folded or lumped or looped and left the rest adhered to the mold.

i wasn't able to find wallpaper paste cheaply in my area, but i do have an artsupply store close by, so i went with claycrete papier-maché, a product i'm familiar with from several other projects.
i mixed this very dry, as dry as possible while still maintaining some amount of plasticity - a little like a fibrous modelling clay in consistency. but the water content *still* seeped through my paper-towel lining, completely soaked my plaster mold, and totally ruined it.

so, giant waste of time and money. i'm normally one of the biggest and loudest proponents of DIY EVERYTHING you'll ever have the questionable fortune of running into, but in this case, i think it would have been a better idea to actually pay to have the form made.

next time i try this, i'll use the foam. it would have been cheaper, frankly.