I've tried all the different methods on Espina, starting with a tarp, next was shrink wrap and finally a custom built cover that fits over my cockpit.
The tarps are great for about 2 months, then the wind
gets to them and they start to come apart. At the end of the season your tarp is no longer water proof. I spent $375 on a standard 35x20 foot tarp, silver inside, black outside. By the end of the winter I could sit inside and see millions of pinprick holes in it. It did keep most of the water off but I figure it was toast by the end of the second year.
After the tarp died, I went shrink Wrap. At $11.50 a foot, I think the bill came to about $365 for one winters worth. They did a beautiful job, a door in the side,and 5 vents. Never a drop of water to be found. Plus with the sun shining on it, working on deck was tee shirt work. Below it raised the temp to about 50°f on a freezing day.
The second year the price
went up, and I paid about $415. This time when the season was over, I very carefully cut the wrap loose, folded it up and reused it. Net cost $207 plus about $20 worth of tape.
Third year we got a bunch of us together and did it ourselves, by buying
the plastic, tape and ribbon from U-line. The torch we bought was a cheapy from Princess Auto. Net cost that year? $120.
Finally when I started working on Sabre
Dance, (Espina was now gone) I realized that to build the frame needed and the plastic to cover her would be much more expensive I did some math and came to the conclusion that a custom cover amortized of the life of said cover was a better deal. A full cover would have cost me about $2800 but I ended up with a half cover which encloses my cockpit from the wave breaker just ahead of the main hatch
to the back of the boat. That ended up costing me $1200, and amortized over 8 years, is $150 a year. It too keeps the boat dry and being darker in color also helps with heating
in the winter. One minor niggle is that it flaps a bit as the wind blows. The shrink wrap never does that as it is band tight.
So there you have it.