Spaf:
Mud-Dobbers are a true pest. Here in WA. State, we have more of a wasp problem, but hornets and dobbers show their ugly heads from time to time.
Although I hate doing it, every spring I take "everything out of the boat and pile it in the garage. It's a chore and a pain in the a##, but once cleared out, I close up the water tank and bomb the boat...sometimes two times..that stuff kills a lot more than fleas..
When I wash the boat, I always power spray under the area where the deck is molded to the boat. There is usually about two inches of space where all sorts of little critters find their way into laying eggs, then I apply bug spray (Ortho) in that crevice.
That usually takes care of things for a while..but what amazes me is how after a few days on the water, at the mooring buoy, about 100 feet from shore...I can row out to the boat and find a spider's nest on the outboard, or on the stainless steel guardrails..
Good news for me is that the interior seems good...no problems I've seen.
Birch is right about spiders..but they give me the creeps and I really don't enjoy sharing any space with them. The dobbers are a problem for all boaters in the midwest..I have many friends who sail in Iowa, Oklahoma, Missouri, and Arkansas, and they all attest to the nuisance of the dobbers..
And with respect to the brown recluse...well...it just gives me the willies even thinking about it..
I'm sure you've already tried all reasonable approaches but I thought I'd share what I do ...Good luck Spaf...
Oh, and one more thing...I get the itch to get out and everything goes positive again in the markets today....Oh well, at least I didn't lose anything...I'll have to look for my next entry point..
FS