Defender carries 3 mil (.003") x 3" wide, which I see is what HamRadioOutlet that Rodd suggested carries. One nice thing about Defender is they sell by the foot, some of these other places sell only 20 and 50 ft increments.

I'd consider going a bit heavier. I just found a place called basiccopper.com that sells 5 mil in 3" widths. Unfortunately they only sell 20 ft or 50 ft lengths but in the scheme of things the cost isn't a huge factor if the heavier mil will last longer.

(McMaster and Grainger also carry 5 mil but only in 2" or 4" widths. I don't really want to go up to 4", it's already enough of a nuisance to run the 3" and you slit your hands when you have to reach past it to get to the bilge for instance).

Has anyone used 5 mil?

Thanks for the other suggestions so far.

Max