I've recently installed a new heating system in my Willie 16. (You might check this BB, I put a post on about a month ago re: heaters.) The two & one half gallon tank goes behind the rowing station. I took the tank and boat to a porpane dealer, showed him the heaters, and where I wanted the heaters, and he cut the hoses and attached the fittings. All totaled it cost about $50 and I had no leaks! I spent a bit more for brass screwin caps so I can leave the hoses in the boat during the warmer parts of the season.
I took my boat to work (where there's a welding shop) and had two unique brackets fabricated. They are hard to explain w/o a drawing but I'll try. They include a battery post clamp welded on a short upright piece of Aluminun, welded to a half piece of Al pipe slightly larger than the diameter of the rowing foot support. I used a piece of ABS black plastic cut down 1/3 for the other half, and two large hose clamps to attach the rowing station heater. Be sure to leave enough hose so the heater can be moved side to side, it also swivels. (I fished twice last year in the snow & the guy in the front had my portable heater--usually rowing keeps me warm enough, but there are times I wish I had a heater, also portable didn't fit well near the rowing station). For the front, I still working on the design. It will be adjustable under the "fly" or front deck. Again, it includes a battery post clamp and a rod that extends thur the clamp for movement forward and aft, and another battery post clamp for side to side movement. I found that too much heat build up under the front deck if the heater was located under the fly. I'm currently looking for a smaller heater head, the Mr. Heaters are too big, something in the 2000-5000 range would be perfect. If you or anyone else that reads this knows where I can get a smaller heater, please let me know. Mr. heater stopped makeing their Mr heater JR.
I exchanged emails with a guy in Oregon that had a different set up. Email me or call if you have more questions.
PS I called Willie and asked for their advise and they recommended an external hose system as opposed to an under the deck system.
It's a good project for when the rivers are out. Good luck!