How can i attach aluminized Mylar to a sheet of PET?

We are building a parabolic solar hot water heater and are using a large (4' x 8') sheet of PET as the base for our parabola.  We have been trying different adhesives to attach the large aluminized Mylar sheet to the PET base.  We have tried various methods but are still looking for something that is more liquid than adhesive in order to be able to place the sheet.  We'd like something that's about the consistency of liquid soap (maybe this would do!) that we could spread out with a roller, place the Mylar on top and using a clean roller, roll out the bubbles.  We were thinking about liquid soap because the area is large and the cost of the soap is low.  We've tried everything from axle grease (not bad) to two-sided tape (not suitable because we'd have to tape the whole area).

It seems that most adhesives are pretty expensive in large quantities and when applied, dry really fast, leaving us unable to move the sheet around in order to place it properly.  Most of them also leave residue which cannot be squeeged out.

Any suggestions would be greatly appreciated.  Here's the URL to the website:  http://www.appropedia.org/Anisa_Foundation_parabolic_solar_hot_water_heater

Have a great afternoon!  

Check out this guide to solvent welding.

Thanks, John!  That was a great page.  It appears that i need Acetone.  i will have to try a small amount on the Mylar as well, since i only want to "melt" the PET and not the Mylar.

i also suppose that it will need to be applied with something like a paint brush on a small section of the PET and the Mylar placed over it and smoothed out and then more Acetone applied to another section and that section covered with Mylar.

Again, thank a lot for replying and have a great evening!