These are Marine grade two piece 100W jobbies, the larger part being 6inch, that I found on the bay for not a lot of cash.
Made the surrounds myself.
All the connectors on my std car Amp are covered in silicone grease, and I've sealed up all the holes/gaps in the case with the same stuff.
It all survived last Winter and I've no reason to suspect it wouldn't last a few years. The jack plug for the MP3 lives in the glove compartment.
I'm also looking at a cheap source of some bigger speakers, as I have a choice of two more Amps sat in the garage now.
1 x 500W/C and 1 x 800W/C.