Hi.
I just redid the loo area in the LDV. I'll take a pic and measure it if you think it'll help, but what I was actually going to say is that the height of the loo off the floor level is a factor - if its raised you can get away with a bit less floor area. (I kind of stumbled across this by accident and necessity, not through being clever like nbrown though
!)
Now I've moved the walls about a big portion of the 'floor' of the loo space is now taken up with the whole rear wheelarch (Sully is twin wheel axle too, so bigger than your Boxer wheelarch). But.... this turned out to be an asset if anything.
I boxed in the wheelarch and made it so it was wide enough to take the Porta-loo thing facing across the van, with a baton-type lip on the front edge to prevent it sliding out of place. There's enough real floor left for your feet between the boxed-in bit and the partition wall. Because the loo is now more sort of house-loo-height, then you actually need less space than if the loo is placed straight onto the floor, cos your legs don't have to bend as much as if it was lower when you sit on the thing (before the loo sat straight onto the floor level in our van cos the whole cloakroom area was further forward).
Also - a wheelarch area is dead space anyway that gets lost in a cupboard or similar anyway cos you cant stand on it - so a loo support seemed as good a use for the space as any to me.
I've also used rolls of the stuff they stick behind radiators (600mm x 10M bubble-wrap/foil sandwich rolls they flog in B&Q, Wickes etc. - same sort of stuff I used to make my 'silver screens' glued under under the boxing-in and on the walls so the hab area has extra insulation from the storage/utilities area in the back of the van.
Also my door/wall between the cloakroom & hab area is angled to maximise access/space in the hab & minimise the space the loo area takes up - so in transit I can slide the loo into the front 'corner' where it's snug and secure, then slide it back into the centre when parked up.
Its not fully road-tested yet cos I'm still faffing - but I haven't used much space and its got room enough - I'm not a big bloke but I'm 5' 10" & not small build at 13-ish stone.