Chris,
Yes you are right, fiberglass can absorb up to 1/3 its wieght of/in water. But I have found ( in repairing Marks boat) that the Dart is "laid up" with high quality cloth and workmanship, and if you keep it dry it will be OK.

Keep it stored OFF of the ground (on nylon carpeted blocks) and covered/tented so that rain is shedded off and air can circulate it will dry out. Remember to tie it down so it will not flip over while stored

Mark is in NYC w/girlfriend, I'm waiting for a call back from him

Harry