I have a Yost Seapup covered in vinyl. It has help up fairly well. I reskinned it last year.
Vinyl comes in various weights. I think boy scouts will punish anything you give them. I would try to find a heavy vinyl (boat will weigh more). If there are sharp objects you will get small cuts where the vinyl crosses the chines and keel. I patched them over and over, but patching is easy. Most of the cuts we got from oysters in the Hood Canal. I would also double layer the fabric on the keel and chines - that helps a lot. I just run a 2" wide strip for reinforcement.

Are the boys helping build? I would let them. It will give them some respect for the boats and they will treat them better.

Good luck!

Foster
The picture is my nephew in a Sea Flee we finished last July. I got the vinyl at a local tarp manufacturer. It pays to look around. Price was good and availability way great.
P.S. Two part urethane over nylon is the best (easy to put on, reasonable price) covering I have heard. Vinyl might be less expensive, but not as tough.

: I've just started building my first kayak using pvc. How strong are
: they? I've watched videos of guys rolling them, but how well do
: they hold up to rocks and underwater logs? I'm planning on
: building about 7 of these with my Boy Scouts this Winter in
: hopes of taking them down the Wisconsin River in August. I
: really don't want to build them and then find out we should have
: used canvas. Any thoughts?

: John "Rock" Rockefeller
: Scoutmaster Troop 747
: Waupun, Wiscosnin USA