Who fitted your tank. I learned today that the connects have a double floor so fitting tank not straight forward?
I've got a connect with 500 Litre grippatank I fitted myself. It's only got bolts through the floor brackets closet to rear door at the moment. The front is right up against bulk head. A rathchet stap round tank and frame to hold it all together as no bolts in front.
However I noticed the other day behind the driver and passenger seat there is a hole through to what would be the rear passsenger footwell. I've not tried it yet but I think it would be an option to fit front bolts.