It was installed in the rear passenger seat floor. Makes W&B simple and I intend to use it 1-up dong acro. It will remove quickly to reinstall the seat cushions.
You put it in the battery box spot too!! For my RV-4 that was the only place to go for weight and balance purposes. I love it, never have to worry about back seat weight, if they can fit between the longerons I'll be in CG! (I'm joking, I do check their weight, but this is pretty close to accurate).
My tank is a little "above" where yours it, it extends up vertically about 6 inches, ended up with a little over 4 gal of smoke oil for airshow routines. Great minds think alike on smoke tanks!