Our trailer is a 2013 and we have the installation instructions too. Yes, its the Dometic/Sealand.
We can see the access but getting to it is the issue. We can see some of the attachments but getting a hand, let alone a tool, in there is proving pretty tricky, so wondered if anyone had successfully gotten in there.
We were looking at it again today and joked that we should just leave the toilet in place and just sell the trailer.
It could be a bigger job than we thought!