[Geo]

The spare tire location on a Transit has a 5" steel floor beam above the tire that the tire crank down mechanism is attached to. While the spare tire and crank down mechanism can be removed, the floor beam is an obstacle that you will need to work around. There is space on either side of the floor beam to fit either one or two tanks against the floor. You might be able to install two thin tanks above the spare tire, with a limited water capacity and still keep the spare tire in the factory location.

I installed an Onan 2.8KW RV generator in place of the spare tire. My spare tire is stored under the bed. The gray tank is installed under the floor on the driver's side of the van, next to the fuel tank. I used a Custom Roto Molding model H-79 tank that has a 15 gallon capacity. You will need to make a supporting frame to attach the tank under the van floor, as shown in the first photo. Trying to figure out how to fit everything in the van is like a 3D jigsaw puzzle...

Amazon.com: Custom Roto-Molding H79 RV Holding Tank

 

[Geo]

Thanks for the info, tip and link. When you used the void next to the fuel tank for the custom Roto-Molding, did it block/cover the lifting points of the van? Like you said someone has to be a master 3D tetris player to get things to fit in right.

Installing the tank in the location I used will block one of the van lifting points. Same thing for people who install a propane tank in that location. So far, it has not been a problem. When I had the giubo recall done, the dealer just used a drive on lift for the van. They said they use the drive on lift for all the larger vehicles anyway, so it was not an issue. When I rotate the tires, I use a shop floor jack and jack stands.

 

[Geo]

The Onan 2.8 KW generator has all the servicing from the front of the generator, which actually faces to the rear of the Transit when installed. The oil fill/dipstick, air filter, and spark plug are all accessed from the removable front panel. The oil drain is on the bottom of the generator. Even with the floor beam obstruction, the bottom of the generator is still above the bottom of the rear differential, and well above the shock mounts.

Onan just came out with a new quieter model 2.8 KW inverter generator, but I suspect the servicing access is very similar to my model. These generators are designed to be installed under RVs.