And now for the day's activities: By the time I got back from the swap meet (which sucked, BTW) the garage had been at 72 degrees for 24 hours and the drywall mud did NOT come anywhere near drying. I believe that, when used on drywall, the gypsum board sucks the moisture out of the joint compound. In my case, the plastic held the moisture in (and a bare roof would have done the same thing). I tried a high-powered hair dryer and although it seemed to help a little bit, this was going to take days.
Using the 1-mil plastic was a fail in general -- although I would have made it work -- It slid around too much and would have caused cracking of the mud at the edges.
Take 2: I ripped out what I had done, re-cleaned the roof underside, then covered the inside of the roof with duct tape:
The reason I used the duct tape is that I bought 3 large rolls at the swap meet for $5 (like $1.66 each). I know it'll be fine under the mud, but I'll be doing a test tomorrow to see how happy it is with resin poured on it. I may have to switch to masking tape. (Have you had any experience whith duct tape Ogre?)
What I've learned since yesterday is that there's this mud called "setting-type joint compound" that has as one of its ingredients plaster of Paris. It dries chemically rather than by air drying. Tomorrow I'll smear some of that schmutz around and see if I can complete the mold. My Lowes has 3 drying speeds: 20, 45 and 90 minute. I was lucky enough to run into a drywaller at the store and he claims that it's a lot faster than that, so I got the 90 minute. Tomorrow should be interesting...