Had a tank professionally installed through floor what a nightmare when I sold van and tried taking tank out. The petrol tank had to be removed the bolts were twist inside when undoing them from outside, so had to squeeze myself down side of tank with spanner to hold but while mate undone nut from under the van. Sooooo much hassle, would have been a nightmare if I had to move tank to put in hired van if my van went wrong. I will never have tank bolted down again. I've got a 450 tank fitted into metal frame with skid plate, it's ratchet strapped down and push up against my STEEL bulkhead so not going anywhere. Had it like that in my other van for 4 yera and my transit custom for over a year. If I need to take it out I just undo straps unwire from van battery and slide it out with noooooo hassle 👍👍👍😳😝