I had trouble finding something to set my cage on as well and ended up finding this table at Staples for a good price. I plan on using a 40 gallon tank when my snake gets bigger and it should fit perfectly. The dimensions are 36"W & 20"D, which basically fits a 40 gallon exactly(36"W & 18"D).
http://www.staples.com/Staples-Easy2...product_951560
But really you can use whatever you want if it is the right dimensions.
Also to note, the Zoo Med pad that you showed above does come with round rubber pieces that you put on the tanks corners, which raises it up a little bit to allow for heat to escape and room for the cord.