Well, after 5 years, I thought I should put the finish on this thread. It turned out to be more than a year before I got the underlayment and carpet back into the car. For a while I just threw in some indoor / outdoor carpet that I had, and drove it that way. Then one day, trying to leave home after a flood had washed out the road, I bashed a baseball size hole in the oil pan. So, I had bigger problems than the carpet and underlayment.

After washing the antifreeze out of the underlayment in the bath tub, it didn’t want to dry. I think maybe it is closed cell foam, which once saturated, doesn’t want to dry. I hung it out in the hot sun for 5 days. It would seem dry, but if you pressed it with a tissue, the tissue would end up wet. Finally I locked it in a small bathroom with a dehumidifier for about 3 days. That did the trick and it was finally dry.

To patch up the broken rubber cover that is on the underlayment, I cut the broken pieces out so that they had straight edges instead of jagged edges. I went to a home supply store and bought the most flexible peel and stick “linoleum” floor tiles that I could find. I cut them into patches to fit the areas missing the rubber facing, and they did stick into place, and were about the same thickness.

To cover the joints between the patches and original material, I used the peel and stick type of duct tape that is made of heavy aluminum foil. Don’t confuse this with the grey cloth duct tape.

Then, to put the underlayment back into the car, I taped my cut joints with the same aluminum duct tape.

So, it did all work out in the end.

Thanks for your advice, Klaus. Maybe this thread will be a bit more useful to someone in the future now that it relates the conclusion. Better late than never I suppose.

Charley