Only on the older Betrams,,, the entire cockpit deck could have rotting problems. I believe they made the decks out of a product called or they called "Nidacore". I could be wrong but I believe that's what its called. Also Iv'e seen a few where the rear Bulkhead develops soft spots, which if that's the case it's an easier repair than some other boats because the tackle centers are not molded in but rather set and screwed into place. So they can easily be removed to get to the bulkhead. Also like you mentioned they do get salt in engine rooms I believe from the type of air scope vent sticking up of the decks.
Don't get me wrong, I'm not knocking the Bertrams. I think they're great boats and would be proud to own one. I was just trying to point out the differences and things to look for.
That being said if you can find a nice clean 42, 43, 46 Betram don't be afraid to jump on it. Those are all nice looking, great riding boats that are over built and able to take on any sea your willing to go out in.
I'd have to say the 46 is my favorite of that era, nice low cockpit freeboard, high bow and overall great looks. Next step up in size and price I'd say the 1987 and newer 50 Bertram, but thats a whole different discussion.
Tony