Spotted one of these towbar platforms today.

[mark61]

Looks pretty good to me, could be just what I need.

I tend to use back doors, can it be swung out the way to facilitate this?

Came across a few that still allow use of back doors when I was looking. Never got one though as pricey, decided to leave more stuff at home.
Sure I came across a few made in USA too, similar money or more. Not saying they aren't worth it as they are all appear substantial and well made.

Van-Star Swing-Away Cycle Carrier - RoadPro

Busbiker

Steve of Herefordshire's Van Build Click on bike rack on menu on the left.

 

[Byronic]

Sometimes the only way is to fabricate your own solution.
Carrying a mbike or a large box and being able to access barn doors
seems to need a custom solution. I couldn't find an off the shelf system.
Mine works ok when parked up for more than a few minutes because it is
wound out on a screw thread it takes a few minutes. I did motorise it but the
electric motor terminally corroded, so for time being I just use a 12v drill.
The rear doors can be opened sufficient to allow access for non pot belly
physiques!