I finally got around to do doing a bit more over the weekend:

Plastic card to cover the Pringles tube and form the rear hull.
I have embossed it from the inside so that (hopefully) it looks like rivets.

More plastic card was embossed to form the skin of the conning tower.
A topside deck was made from foam PVC and chequerplate plastic card.

The black part of the deck was from a car air freshener& looked suitable to use!
The hatch is a metal one I acquired ages ago.....from somewhere.
The side observation pods are the container from a chewable toothbrush....no really!?

The tail is foam PVC with a propellor cut down from the car freshener

The whole sub.
Minor filling & finishing off required prior to painting.
