I made my own whelping bed. There is a pocket for the heating pad on the left side of the bed. The walls are high enough that the babies won't get out and my Raeley can jump into it. It give her enough room to have the babies on the right side without getting over heated. I still need to add the door, but it will have three heights. It will lay flat when the puppies are old enough to explore, it goes half way up to give nursing mamma easier access and to keep the new puppies from falling out, and it goes all the way up when the start getting more mobile. Here is a link to see what I have so far, it still needs some improvements but I still have time to correct that before she has her litter.
Whelping Box pictures by MntSnowBabies - Photobucket