There is a small forest inside the 330 SS . . . no liner. Fastecs and super sports have the liner. . . PC's and Sun Sports are old fashion wood with glass over.
If the center stringer has high moisture, as most do . . . , I would also check the main bulkhead that the stringer mates up to. The center stringer on the 280 & 330 SS are basically hollow, made of 3x2 dimensional lumber and 1/2" plywood, then glassed over with about 1/8" thick of CSM/cloth.
The engine mounts are through bolted (not lag bolted) through the center stringers and the 2 side stringers. If your engines need alignment, then it may be an indication that the stringers are starting to give-way to moisture.
My boat had moisture in both the center stringer and the main bulkhead. The bulkhead was worse, so I replaced it, but the center stringer, although somewhat wet, seemed OK.