Steve, for what it's worth, I've hung my Dirigo 17 (fiberglass) from rope slings for 24 years now (in the garage) and it's just fine. Webbing would be even safer. If you're going to keep the boat outside suspended from A-frames, why not staple or nail up any kind of sheet goods on the A-frames to serve as a roof over the boat? Keep both the snow and the sun off.

Carl