Stanton spare wheel

Just bought a new Stanton. Was aware no spare which concerns me a bit. Asked dealer for possible options & they said A-S can re site fresh water tank under seat inside & fit spare wheel carrier where tank is underneath at a cost of £1600. This obviously takes away a lot of inside locker space so I'm not keen for that reason & the cost. Since getting van noticed the waste tank is at rear underneath. Surely the easiest answer is to remove waste tank, join all waste hoses together & use a slide under caravan waste carrier. In place of waste tank fit a spare wheel carrier. It looks like you could almost have the rear panel cut out at number plate level & make it a hinge down panel (bit like the wet side locker door). You could then have a tray behind to slide spare wheel into.
Other than that it's have a tow bar frame fitted without the towball. Then have two vertical arms with the spare wheel mounted on the inside of the arms. So it would be at a position on back of van similar to Auto-trails & hinge down to remove wheel.
Any ideas or thoughts?
Many thanks

Some ideas:

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Thanks Mojo - I had looked at these posts previously. The mod done by Pete Taylor has the wheel low down on a tow hitch with bike rack above. Im not having a bike rack & would prefer wheel mounted higher up out of the way partly in the back panel recess with it hinging down.
Thanks for link.

If you decided to use a slide-under waste water tank, where would you carry it? With even the best intentions these things get stinky if used in hot climates for a while.

If you start chopping bits out of the bodywork you will invalidate your Auto-Sleeper guarantee.

I've seen a Stanton with a spare wheel mounted higher than mine on a purpose-made frame; this was attached to a tow bracket (without ball) in a similar fashion to my set-up. there was no-one with the van to talk to. imho (Mech Engineer in a former life) mounting a huge weight like a spare wheel/tyre/frame at the height of the indentation under the rear window would adversely affect the handling due to the considerably raised roll-centre/centre of gravity.  Without suspension modifications a fully-laden Stanton can already corner like a galleon in a gale, so I would not want to alter the roll-centre to a higher position.

My spare wheel for my 2008 Devon is in the nearside locker. As it is too wide to fit in this area normally,  a previous owner achieved this by cutting into the interior side panel and boxing it in. This results in a slight projection into the area between the lounge seating, but it is not a problem. Tyre is accessed from the exterior locker.

Hi FOA. Thanks for your post - that's another possibility to think about. It's probably the easiest & least costly to do.
I think my favourite idea at the moment is to remove the waste water tank behind the rear axle at the very back of the van. Use a slide under waste tank & have a spare wheel carrier made to fit onto the Merc chassis legs (where they usually bolt on extensions for tow bars). So the wheel will be laying flat under the rear of the van. Will have to get some costs & way up the options. Cheers Aldercow