Right!

I have just returned from B&Q, with a 2 meter bit of insulation.

It is 63mm wide (diameter), and the hole is 16mm. I now need to mke it into sponsons. One question I havefr trict, is on your pictures, on diagram 'fittings 2', on the cross section sideview, what is:

The rectangle with the solid black outline,

The shaded item that is inside the rectangle

and also, what is the plastic tubeyou mentioned? Is this the black rectangle? Also, can the yellow thing be made out of 1mm aluminium?

Many thanks,

Andrew