To assemble, the lid is taken off the small and medium boxes, the walls are 'unfolded', stood in the box and lugs in the base are pushed through slots in the walls, the front 'flap' is folded down which forms the dam's entrance way. The corners of the waterproof sheet are then pinched together and folded towards each other on the outside of the formed tray. The tray is then slid down into the box which forms a waterproof base and also holds down the fixing lugs and the front flap. There are perforations below the front flap which can be torn down as the puppies get older so they can get out of the box.

Pig rails for these boxes, if required (and they rarely are for the small box and it also depends on the breed of dog for the medium box) come in sets of three and they are made of wooden doweling, 22 mm dia. The doweling rails, slightly longer than the width of each side, are threaded through perforations in the walls (it's best to slide from the inside out, pushing one side through a little more than required through one perforation, then sliding it back through the opposite perforation).