Hi.....Now this may sound unusual, but I had spiders all over the inside and outside. Spraying w/ bug killer to no avail. Inside the mainsail boot, under the cushions, etc. I gave up.
I wanted better ventilation inside the boat, so I bought 2ea. 120 volt 6" fans and kept them continually running while at the dock. Since then I have seen 1 spider (big) inside my toolbox, and a smaller one on the deck. Coincidence? Dunno, but maybe it is the air circulation, or the humming, or the 120Volts, but it appears to work, and for 3 years now. Got the fans at ACE Hardware, but am sure they're avail. all over. Jim Huhta S/V "Sea-130" 1979 C-27 TR, Sturgeon Bay WI