[Christ]

Well, you can do it with lexan too, but IIRC, polycarbonate lets off fumes that you don't really want to be breathing... and it's very soft as far as polyplastic materials go, so it's quite easy to just use some clear oil (think: WAHL haircutter oil) and a tap, and a little patience with Lexan... Plexi will almost always crack right near the end of the project, b/c you'll slip up thinking you're in the "Home stretch" LOL.

The melting with screws thing is a way to cheap out on something if you can't get Lexan for cheap.

Inversely, if you don't worry too much about weight, you could find a house being remodeled (check craigslist or freecycle as well) for an old breaker box, which you could cover with a single sheet of polycarbonate or plexi.

A friend of mine pointed out that if you use a high-speed drill/driver, and you have a bit for regular (not self tapping) sheet metal screws (just pointed screws, like you use for aluminum down spouts), you can run the driver in reverse and give it some pressure against the plexi, and it will "burn" it's way into the plexi and set there, so that you can extract it later.

Doing this does weaken that spot in the plexi though, by "work hardening" it, which means that spot won't flex any more, and may crack over time from vibration.

On the plus side, if you're using a breaker box or something similar, you only need one sheet of plexi, which you can (very slowly) drill holes through without having to cut threads into it. Once the holes are drilled, use a countersink (again, very slowly) on both sides to lose the sharp edges, so that it's not as prone to crack, and you should be OK with it until you get some Poly... poly or acrylic sheet is definitely what you want in the end though.

Sorry for the long, if not helpful, post.