I'm not crazy about the idea of moving the tank up into the port locker. That's about 175–200 lbs. of weight that you'll be putting there when the tank is full, and you're removing about 150 lbs. from the bilge. However, if many people have made this modification without problems, it should be okay for you to do it... and then you could convert the space where the existing tank is into additonal space for batteries... and make a larger house battery bank.

__________________
Sailingdog
Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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