An alternate to a giant coachbuilt would also be a simple van designed to hold a lot in the garage, such as this Adria that Andrew Ditton shows us around:
If the mobility scooter can fit into there (or change it to one that does!) thsi would give you a nice manageable solution.
Too gimmicky for me that, using power as well to raise and lower the bed
Fixed bed better with space underneath, I like the La Strada Regent S but fridge too small in it and it's expensive as on a merc base, great length though at under 6 metres.
CS reisemobile Rondo or independent excellent vans but again so expensive but they will build the rear bed as high or as low as you want