I'd expect it to be either in the bilge area near the fresh water plumbing, or tucked away in the mid-berth. My old 280 had an access panel at the end of the mid-berth. The water heater and A/C were behind that.
Check engine compartment, ahead of the water tank. You'll probably need to put your head into the compartment and look up toward the bow, it might be under the floor in the middle of the boat.
Answers
2002 FV 342 on Lake St. Clair - Past Commodore SHC - Vessel Examiner USCGAUX
Boat Name: King Kong
"Boat + Water = Fun"
Go Steelers!!!
Andy