Hi steve C,
I've sailed the new Serenity with a 42 cm Tangent Dynamics "Reaper"
weed fin in Pine Island Sound in Florida.
It worked really well and the upwind angle and speed in very marginal conditions with a 7.5 m2 Retro was nothing short of incredible.
I see no problem using weed fins in the Serenity.
I'm going to try some larger and smaller weed fins as soon as I get back on the water in Hatteras.
I tried a smaller 58 cm DeBoichet Concept and a 5.5 m2 Retro last weekend and compared to wider boards that were only able to plane at the height of the gusts, I was cruising right on by them most of the time.
The Serenity was by far the fastest board on the water in the 7-10 knot winds on Sunday.
Hope this helps,