I managed to get the rest of the hull sanded and a second coat of highbuild on today. The underwing side of the hull sanded really easily (as easy as sanding can be, which is still hard work) and was a little fairer than the outboard side (ironic really). I used a fine roller (foam) on the second coat but surprisingly (to me) I used the same amount of highbuild on the second coat as I did using a coarse roller on the first coat. I had just a little left in the tray when I got to the end so I just went over a few of the poorer sections and used the last of it. I should be able to get a good finish with 120 grit paper and will then apply a final coat of highbuild. I think a final coat will equate to half the 20 litres I have so I will get both hulls done with the highbuild I have.
With any luck I may get this coat of highbuild sanded this weekend and the final coat on, and during next week I will get that sanded with 240 grit which should make the hull very smooth and then I will be applying 2 or 3 coats of resin mixed with copper powder to the underwater area to 100mm above the waterline as an antifoul base. Then the hull will be ready to turn over.