Best location for the tank depends on...
Where the head is located in the boat. If it's forward, the best location is under the v-berth...if it's aft, the cockpit MAY be the best location...or may not be. The tank should be within 6' of the toilet. I'll help you spec it out if you'd like to email me. I'm in all the owner directories...you can email me from there.Meanwhile, you should find the link below useful.