I'm installing a layflat 650 in my van next week, and was considering having it about 2 foot from the rear doors. Just enough space to put the safety cones & reel etc inside the back door. I've checked the axle loading info and even though the weight is mostly over the back axle it's still well within limits for my van. The tank will be in a custom built cage and secured to the chassis. I've not got a lot of faith in the bulkheads,.. they're secured by only a few small bolts and made from relatively thin steel,... not enough protection to make me feel safe unless the tank is properly secured.
I'd still have a lot of usable space that I can get at from the side door for my office cleaning gear