Hey, so this is my whelping box I made out of advice from all the YT breeders...
I loved it! It was easy to clean, easy for mom and was convenient!!! The top could also be taken off for easy access.
Also, when I no longer needed it I cleaned it up, packed all my whelping supplies inside and have it ready for my next litter. :P
Here is the link to it...Good luck with your box! Congrats on the litter and kiss the momma from us :P
http://www.yorkietalk.com/forums/showthread.php?t=59234