Hi all great site with lots of info The wife and i looked at a few Adventure products over the past weekend 86fb,80gs and the 80rb we liked all three but think the 80rb will suit our needs the bes...
Did some informal testing using an Oxygenetics shower head (great pressure/low water use) and with mixing hot & cold water we could have 15 min. of non-stop showers with a 6 gallon water heater. So I wouldn't worry too much about a 4 gallon one. Probably plenty of water if you are OK with "camping" and not looking for a 5-star hotel experience LOL.
Personally I don't mind the trade off of lower capacity tanks vs. weight for my type of camping.