Need waterproof tape

This may be kind of “off the wall” but I have an old fiberglass deck boat and there is a leak where the top cap and the hull are joined – under the rub strip. The gasket what was there has apparently failed. Is there a waterproof tape that I can apply under the rub strip across the two sections that will seal the leak. This is behind the motor jack plate and would require removal of the motor mount to do any other kind of fixthanksjwt