You can see our set up here
https://new.livestream.com/accounts/...events/2372631
We use a open ended box made from 4 foot sheets of MDF. Into the box we build a smaller compartment in which the mother can nurse the puppies. This has pig bars on all four sides so that the puppies are protected from being squashed against the side of the whelping area by mum.
We remove the bars once the puppies are moving around and have sight or as late as three weeks when they are starting solid food.
This allows them access from the nursing area/bed to the rest of the main box where they first go to the toilet and eat.
We place an open crate in the whelping/sleeping area so the pups get used to a crate.
We put lino and paper on the floor of the box and the whelping area has vet bed and a heat lamp/pad depending on time of the year.
Mum is able to come and go from the whole box as and when she wants.