Go for it!

I'm not fond of 1/2 inch pvc, but you might try 1 inch for keel and sheer, and 3/4 for longerons.

Lay out your frame patterns on plywood and drill holes for the tubing first, then cut out the frames, notching into the holes, so you leave about 3/4 of the hole intact. this leaves the skin rubing on the smooth side of the tubing instead of the rough edges of the frames. taper the tubing where it meets the bow and stern frames by cutting the inside edge of the tubing and attach it with recessed bolts.

Stagger the joints