As kcassells mentioned, 3M makes some good stuff for automobile trim. I think the trim on my old truck is put on with double sided tape and it's 22 years old and still sticking...
By the way your asking a lot of the glue at 25 years.. most of the rub rail I've seen fits into a plastic or aluminum channel and the rubber shrinks a lot in 25 years...
Thermostat housing is where the boat gauge gets it's temp so that's a good place to start but while you're at it you might as well check other areas...and yea the if thermometer would be fine...
The impeller cannot prime itself, it must have water forced to it with muffs. Alternatively the drive must be submerged in the lake deep enough that the impeller is below the surface..
