We have had blisters for eighteen years and repaired them one each haul out. Therewere only a couple of blisters when we bought her. But after moving her to the warm fresh delta water she blistered like the pox. We had a blister job done in 2008 on Mexico at @$5,000 here they peeled off the gel coat. In 2012 we hauled to do the Dave King mods and found the hull blistered again. Unfortunately they had used West Systems with graphite and it was harder than concrete. It took three days with a 10" grinder and 20 - 18 grit disc. to get it off
Here's the method we used:
1) Coated the hull with two coats of West system epoxy.
2) Filled and faired the hull with West Systems.
3) Coated again with two more coats of West Systems.
3) We applied 5 coats of barrier coat from West Marine,
can't remember the brand but it is one of the well known brands. Alternate white/grey colors.
4) Applied two coats of Pettit Trinidad bottom paint.
We hauled a year later and had no blisters for the first time ever
The owner of Ladds yard doesn't think drying does much good.
Jim