Originally Posted by Ron in BC
I've sort of done that already. If you go to my post under mods. "Adding underfloor insulation" you can see there's an area just ahead of the grey water tank where there's lot's of room for an additional tank. There's also a similar area behind it. However both are either ahead or behind the axles so balance would be affected.
Great stuff, Ron!
I guess missed your topic when it first appeared, although the subject of insulation and underfloor layout has come up before in less detail.
Direct link to Ron's thread: Adding underfloor insulation
One factor which didn't matter to the insulation board but would matter to a tank is vertical clearance: the top four inches is between the frame rails is available, but additional depth can depend on parts such as suspension. The rearward available location (between stock fresh and grey tank locations) runs over the square tubes of the Torflex suspension. A four-inch (10 cm) tank isn't very deep, but could still have about as much volume as the stock freshwater tank, given an area about four feet (1.2 m) square - less space for brackets and plumbing - to occupy.
Anything not exactly at the axle position (in the case of a tandem like this, the position midway between the axle lines) will affect balance, but not by much when it is this close. The area behind the grey tank and ahead of the stock freshwater tank is right over the axles, right?