Eventually this is what we came up with, with some clever design modifications from Klaus, who built it for me. It's a little difficult
to see in this picture, but it is an A frame shape, with both sides of
the 'roof' lifting up - one side is up here. The door is to the left of
the photo (open). It has no floor, and there are two wheels on one end
so it is easy to pick up and move around.