Doug,
You are right in that there is a cost to pay for the extra large water tank. That cost is of course reduced cargo space and more weight, assuming the tank is topped off (best full so as not to slosh around). For my needs it was fairly easy to rationalize that instead of carrying a couple of extra water containers, it is the same difference to simply purchase a larger fresh water tank and carry it all in one place. Also purchased a countertop PUR water filter so now I won't need to carry an extra 5 gal of drinking water -- I'll just use the one tank for all H2O needs. The space previously occupied by the extra water containers (usually the truck but sometimes the trailer) can be used for whatever else needs to be packed for a trip. Either method has its pros and cons but water volume occupies the same space no matter where you chose to carry it or how you divide it up
. This is why I was contemplating the second couch with drawers to offset the loss in storage, but in the end opted for the two chairs and dresser for a more open feeling. Also, figuring that I could build a replica of the longer couch or factory order the smaller one with drawers and install it later if the arrangement we chose doesn't work out as hoped. Having owned a 2720SL for a short time helped make these choices a bit easier for us -- we gained space with a corner cabinet by the stove, under the sink (no water tank there), what's left under the long couch is about the same as the 2720 we had, plus we have an extra chair and a dresser with inside storage. This will work well for our family of 4 plus 1 Golden K9. Your mileage may vary.
Wade