Damn, I'm sure the wife's enthusiastic support of your hobby just cooled a degree or two. At least it can be pulled off easily enough once it cures, right?
Knowing that hindsight is 20/20, and not trying to sound like an A-hole, for something that big you might want to use a wooden mold box secured with screws.
The guys at Goregoregore.com have a good mold box tutorial with pictures. It's a little overkill for molding smaller pieces, but for something large, it's perfect. Goregoregore.com's tutorials
section is large, but check out the "Molds" section. These guys do a lot of professional sculpting for Sideshow and other companies, and really know their stuff.