>I did use the cardboard type just once. It was OK but not so easy to clean and stains would stay so didn't go down that route again.
Years ago I contacted factories making cardboard boxes. Gave them the size that I was looking for, and asked what the cost would be, and how many I would need to buy. Best decision I ever made. Bear in mind that this was for a toy breed, so no idea how costings would go for a giant breed.
I told them that I was looking for triple layer cardboard and that I would need it to be erected in a 4ft size puppy crate. I've always whelped my bitches out of the whelping box, as that is what they have always shown a preference for. I was able to almost close the box completely, and mum came and went as she pleased. Mostly staying in with her pups. The heaviest blood/mucous loss I ever had meant changing to a clean box on day 3. Very hygienic, as I was able to burn the dirty boxes. I purchased in packs of 10 flat packed boxes. It worked out less than a fiver a box, and I never had a bitch that needed all 10. I liked not having to find storage for a plastic whelping box.