Thanks Mick, you can't beat Tamiya masking tape for the fine work!
I need to add about 3lbs of ballast, now I can place it either side of the motor, but I'm using lead flashing and it did occur to me to epoxy bond the 150mm sheet to the outside of the hull.
I thought it would also make a reasonable scratch protection.
What do the panel think?
In the meantime, here is a springer mast.