Yes Let's (my Wharram Pahi 31) was undercanvassed in light airs. The plans showed a large drifter. I decided to make one from polytarp. This is how I did it.

My drifter is about 22m^2, slight smaller than the plan's 24m^2, but it was the biggest I could fit on the floor. Previous sail making experience was making a few small proa oceanic lateen sails (aka, crabclaws), and of course, doing some sail repairs. This was my first attempt at making a large sail!

I'm surprised how well it worked! of course, I'm more than interested in any suggestions you have for improving the sail. I've used it quite regularly. I'll make another video when I've had it for some times to look back at how it went.