Hi Duane - sorry about late response. Yes, that is fresh water fill. The water tank is just behind there (although needs a thorough clean or replacement - its pretty gross in there...). Happy camping!

Hi, I too have purchased a 1976 1300 Trillium.
Welcome to this site, hope you enjoy your new Trillium. I note that you have a port just behind the door side wheel. Is it a fresh water fill port? Electrical cord ? Mine has a water tank in that side with the filler door over the marker light. Just wondering... Change at the factory? Duane