Here are a couple sites that will be helpful.
Canine Reproduction Video and Book on Breeding and Whelping dogs by Debbie Jensen for dog breeders and Whelping Supplies needed to deliver puppies. eBay Guides - Don't Buy Whelping Kits Make Your Own
I didn't purchase a kit, I purchase all of my supplies at local stores.
I made my own whelping box.
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I am going to try a new pre fab plastic ben with a lid with our next litter, that I bought for under 20.00. It has a pre cut opening in front. Typically used for recycling. You can purchase them at any hardware or home improvment store.
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