I use Permethrin, and works great for a number of things, including no-see-ums.
Will take some on the boat for trips and here's how it's used.
First, spray most everything with it. Have the right solution depending on the concentrate you buy. I always buy the 36.8%, better value and mix 3 fl. oz. per gallon of water for hand spraying.
With this solution, I'll spray everything on the boat, except:
In cabinets where there is food or dishes, electronics or electrical stuff, anything metal (as it will corrode). But primarily spray the floor, curtains, wood, screens and doors. If you hit the window it will wipe off easy. However, don't need to be aggressive inside unless the doors and windows are open without screens.
On the exterior, I'd spray the walkways, sides, canvas (but not eisenglass).
You can also treat your clothes to may them insect resistant and works well and easy. I cut the mixture in half. Mix up a gallon or so, soak the cloths int he gallon, wring out and hang on a hanger to dry. Works well.
Note: When Permethrin is wet, it is toxic, when dry it's fine. It will harm your pets when wet, but generally not plants or some animals, like farm ones (but we don't have a lot of cows and horses on the boat).
This is my number one product for pest control, and will do most everything from no see ums, to flies, misquotes, fleas, etc.
However, my no. 2 choice is a deet product which one can put on their skin, which is very effective, but messy.
CAUTION: Do your own do diligence with this stuff, or any pest control product. Google it, there's tons of info out there.
