I find the rubrails in the plans rather big (25 x 50 mm). I couldn’t find that size, so I used 27 x 44 mm instead. It was quite a job to bend them round the sides and keep ‘m in place with clamps, but I managed. Next time I’d use thinner battens or laminate some layers of plywood.
For clamps I used pieces of PVC pipe cut with a slot (tip courtesy of bateau.com).
small fillet at the bottom of the rails