kevs,
Here's a link to a note I posted a couple of months ago. It was about how I do the very thing you're talking about.
http://luminous-landscape.com/forum/index....c=31080&hl= (my entry is about three quarters of the way down)
A couple of notes: First, no single sheet of double-sided, no matter how heavy, will feel like two thinner sheets mounted together. It won't be nearly as rigid. In fact, the thinner your original two sheets, the more rigid the final product.
Second, you could look into spray adhesives. Yes, they are nasty and, no, I don't know about what they do to print longevity or appearance.
Also, I know there are some double sided adhesive sheets on the market for just this sort of application. It's been a while since I used them myself, but I recall that they worked well, cost a bit more than good old dry mount tissue,were easy to use, and did a good job. I found mine at a local art supply store.
Having said all that, I am using some Moab Lasal double-sided matte for a little portfolio hand-out. The finish is a bit smoother than the Epson Enhanced Matte, and it doesn't feel as "scuffable". I think the stock is slightly heavier and the opacity is good. I'm only printing on one side, though, so I can only guess about how well it handles images showing through the back.
Finally, I agree with tomrock. I think you'd have a pretty easy time finding a used dry mount press if you decided to stick with that option. You don't need a very sophisticated one. With these light papers, I never see any marks if I need to mount large pieces in "bites".
MB