Thanks’ Lars!
Yes - I got an hatch from a local dealer.
Ended up with a hatch from Thetford.
40 X 100 cm.
It was an absolutely good help to see the pictures from Wilfried, - and it was absolutely necessary to flatten out the area where the hatch was to be installed. Way more work than expected, but the final product is good!
I gave started to build up the bed and put a lot of work to move the fan to new location. So far so good!
I will take some photos during this and maybe post my experiences here.