OK, now I'll try to resurrect this thread. Sorry for the delayed response. Some rather, um, interesting computer problems at home sidetracked me...
Larry, you're right: if you aren't obsessed with weight, it tends to add up quickly and somewhat unexpectedly! Even if you are obsessed, like I was, it still adds up. Of course, I made some design decisions in the name of aesthetics or function that outweighed, so to speak, the weight concerns.
I didn't weigh the screws (!), but I did weigh each panel after I epoxied it together. On of these days, I'll add all of the pieces up in my spreadsheet. Based on where I was close to the end, I think I managed to get the whole thing under 1,000 lbs. dry weight.
Not sure why you'd be opposed to cutting holes in 3/4" ply though. The lumber for framing probably costs more than a plywood sheet. Plus, you could use the cut-outs for all sorts of things. I went the 1x2 framing route like you because I had mostly straight lines, but for the front curve and for the door radii, I spliced in some 3/4" plywood. If you are doing a curved profile, it's a lot easier to do it out of plywood.
Scott: give McBeath a call in Berkeley. They don't list a lot of stuff in the website that they carry.
Capitol Plywood in Sacto carries a lot of good stuff. They only sell wholesale, but you can go there and ask to "browse" and then pay a retailer and pick up at Capitol. Hughes Hardwoods (retail) in Rancho Cordova has a good selection of plywood, including Baltic Birch in all sorts of thicknesses. Also, you can get lumber custom milled there cheaper (and more accurately) than the off-the shelf stuff at one of those big orange stores.
You could do a two-step process to make the sandwich. But, I found that the coat of epoxy on the foam and framing, after inserting the foam, was easy and quick. The part that took the longest was applying the thickened epoxy to all the separate "openings" in the frame.
Hope this helps! If you are in the Sacto area and want to see my trailer or discuss stuff, let me know.
Rik