Sid,I just picked up a pint of Bondo brand polyester resin yesterday at my local Auto Zone for about $16.00. The quart would have been a better buy at about $21.00, but since I do most of my glass work in epoxy, I was concerned that the extra material might solidify on the shelf before I used it all. Anyway, the correct thinner is a styrene monomer thinner, which might be difficult to locate, and is pricey, so a suitable alternative is to thin your Bondo with polyester resin. Don't try to reconstitute the whole container of Bondo, just mix up enough for the job at hand. Either the "cream" hardener, or the clear liquid MEKP will work, but it might be a good idea to try a trial batch to see if the cure time is affected. Good luck, Greg