Mark,
Up here in Sitka the vast majority of Charter boat operators shrink wrap their boats at the end of the season. I have asked several of them why they prefer shrink wrap and the reponse was:
1. Walk away from the boat and not worry one bit-"We go to Mexico for the winter and don't want to worry about what we'll find when we come back"
2. Snow sticks to canvas, water seeps through, bugs get in, boat gets damp inside, canvas gets moldy, gotta store it in the summer etc. They feel that shrink wrap has none of these issues.
3. Shrink wrap keeps all the moisture out, even in our cold, wet and cloudy environment, the inside of the boat gets warm whenever the sun shines and it drys the entire inside up.
4. "I can come back to town a day or two before season starts, take the wrap off, fill the boat with gas and I'm ready to go. Before shrink wrap I had to get here a week or two in advance just to clean all the crud out that had grown inside, even if it was covered."
5. "Easy for someone to tell if my boat had been broken into or someone was living inside. With canvas guys would hang out inside all winter and I wouldn't find out until I got back"
6. Critters! We get martins and other critters moving into our boats up here in the winter if we are not carefull. I guess they can smell through the canvas and will chew a hole in it and move in. Take my word for this, sinking a boat is about the only worse situation I can think of compared to a martin moving in for a month or so. I have a great bow picker down on the dock that martin's got into this last year. We STILL do not have the smell out. Trapped the martin but the pelts don't come anywhere near covering the expense to clean that thing out. Not even pure bleach removes the weasel stink. Shrink wrap for whatever reason seems to deter this issue. Local thought is that it is slick, slippery and more difficult to get teeth ito it when it is stretched tight. They also cannot seem to smell what is inside.
About the only disadvantage is that you have to pay every year versus buying canvas once every five years. At the current cost of a canvas cover, you're not saving a whole lot.