Thanks for the input everyone,
I have a feeling that the air in the mattress would be really cold under the foam pad and might not add a lot of insulation but would still make the bed softer. Maybe putting the foam under the air mattress like I've always done with my DAM might add the insulating qualities of the foam pad to those of the air mattress more because the air would warm up more in the air mattress. Its been my experience that sleeping on the DAM is more comfortable with the pad under it and the air mattress is slick so you can roll over without the pad being pushed off the top, so I think I will continue to put the zrester under the air mattress.
Jim