We also filled the composite PP tank. It took 2.89 gal. So with both filled we will have almost 6 gal of PP. Should last a good while. The tank filled is a bit heavier than we had imagined. Glad we went with the two composite tanks instead of one 5 gal tank. It will be much easier to handle on a buss in Mexico and in the dingy.
We are mounting the composite PP tank on the stern and have sold the #6 aluminum tank along with Mr Heater to a dock mate. It is a bit heavy when full for mounting on the rail (the composite tank full). You can see the #6 aluminum tank on the rail under the Sunbrella cover we made for it. We also made the bracket that holds the tank to the rail. Sold them along with the heater etc.