Which GRP single-seater has the lowest cockpit weight?

PW-5 - 121 lbs
A friend of mine, who had similar problem, used to carry a little bag filled
with sand (made by her mother;-), which placed under her...you know where,
added some extra lbs (even 20 ). One thing you should do if you use this
solution is to make sure, that the sand never gets out into the cockpit - it
may cause seizing of some mechanisms and it can end badly. Better if you
raplace sand with some stones (less comfortable, but more safety)

Maciek