How about a mouse pad? Most of us have a couple of extra gimme pads around.
Glue two together if thickness is an issue.
74 Midget, Katy
From: Biff Jones <email@example.com>
To: noel@BATTELLE.ORG <noel@BATTELLE.ORG>
Cc: 'spridgets@Autox.Team.Net' <firstname.lastname@example.org>
Date: Thursday, July 30, 1998 6:40 PM
Subject: Heater Pad
>Another option, Go to an office supply place and look at the
>dense rubber mats for use under typwriters/computer gear. They
>are almost a 1/2" thick and you will have enough to do 3 to 4
>heater boxes. Not as cheap as Franks idea but it will be in one
>Biff, AN6, 'Ole Gray'