I'm going down the 20mm spar route because I've lots of that left over, along with some 20mm foam sheet from a discarded experiment. We don't say 'failed', do we, when we've simply been challenged?
Although the pattern on the site calls for made-to-measure 2' spars, there's nothing wrong with a little overhang because (a) it helps prevent wood from splitting during construction and (b) we'll hang on to some at the rear for reasons to be explained.
I've used four G-clamps to fix the lateral spars so that I can flip it over and apply a line of five screws (one at centre, two at either end and then two more in between).
