I have the Aquacube and like it. I don't have a ton of use, but have taken it on about 3 road trips. It is not exactly small but it does just barely fit in the underfloor storage box/pan. I have a pop up shower similar to this one which folds flat and packs fairly small:
http://www.sportsmansguide.com/product/ ... oClU3w_wcB
and a 7 gallon jug. For easier access, with smart packing I can get it in the rear storage area along with all the gear for 2 people no problem. And I travel with a lot of gear (riding gear, fishing gear, extra sleeping pads, luggage, etc..).
It actually works really well. I can get 2 fairly long showers out of the 7 gallons. The aquacube battery can probably handle ~4 showers? It uses the same green Coleman propane canisters that my little webber BBQ does and that you can get at any supermarket/sporting good store and some gas stations. It is very efficient with fuel as it only fires when the valve is open and water is running through the system. I haven't used it in the winter yet probably in temps down to the 50's and so far I have not had the heat dial even turned up to half-way.
It also gives you the flexibility to leave it all home and save space when not needed for shorter trips.