"Doug Kanter" wrote
What do the manufacturers say in
their brochures or on their web sites?

Most of them speak quite highly of themselves.

The marine stereos I've seen at the local stores don't look particularly
special to me, other than the color and price. Auto stereos have to be built
fairly robustly if they're expected to last any length of time in a car.
There will no doubt be more moisture in a boat installation, but a car isn't
exactly a controlled environment either. I put an inexpensive Blaupunkt auto
AM/FM/CD unit in my boat last year to replace the 25 year-old cheap
AM/FM/casette auto unit that had failed mechanically. (It was mounted with
no rear support and broke at the front support points.) Check back with me
in 25 years or so and I'll let you know how the new one worked out.