Thetford toilet improvement

I'm in the process of renovating my campervan Mavis, base vehicle 1995 Ford Transit LWB hightop and have a somewhat delicate matter to ask advice about. ..ahem ...

Toilets !..    Ever since our first trip it was immediately apparent that the Thetford C200 CWE swivel toilet was set far too high for comfort. It is set on a 4" high wooden platform which is high for me (5'11"  ) but ridiculous for my partner... who at 5'4"  is  swinging her legs .

As part of my current renovation work I am considering fitting a Thetford 400 toilet which I believe has the same panel cutout for the cassette door . The problem is that this would also need to be put onto a platfor for the access door to line up ..

Its become pretty obvious that whoever cut the van opening for the toilet access door didn't know how to use a measuring tape and miscalculated hence the platform.

I have been diliberating over this for some years and haven't really come up with a satisfactory solution which is why the missus is still having to swing her legs. I really do not want to cut a new hole in the van wall and be faced with a difficult and expensive repair and respray job.
Today I suddently saw what I thought might be an acceptable solution. Enlarge the existing hole downwards 4"  and fit a bigger access door such as a gas bottle access door which should fit the larger opening. Ok it won't be the correct door but it looks identical, it won't require any welding or respray work and at least I could then remove the platform and fit a toilet at the floor level .

I'd be interested in any other ideas that anyone might have as an alternative solution and will post some pics when I get around to doing the work.[url=[url=https://s130.photobucket.com/user/peanutNboo/media/mavis thetford door_zps853s2qpr.jpg.html][/url]]