You can probably add a tiny fan to the Thetford enclosure base. Assuming it is a Thetford C260 (look at the label on the cassette frame under where the cassette lives). Remove the cassette and if you have a 40 x 40 mm square hole, with what looks like a pipe disappearing downwards somewhere then the cassette has a built-in ventilation system. One camper I had, had a small fan in this square hole and when I pressed the flush button once, the fan came on for 2 minutes or so. It sucks the rosey smelling de-oxygenated gas from above the sludge in the cassette and pumps it out underneath the camper.
There are two ways of fitting this yourself:
1) Buy the official Thetford kit from Prima, at an extortionate cost of £140:
https://www.primaleisure.com/produc...kyo-D9lWYIs6nU02xgFdUJ5r1DUbazgsaAurTEALw_wcB
2) Buy the fan only from Prima at an extortionate cost of £54.99
https://www.primaleisure.com/produc...FbUk0T4QaioXLcuASONBj5y7IQfDrtzkaAmUqEALw_wcB and connect it to a £10.80 2 minute timer from Amazon,
3) Buy the same fan from Amazon for £10.80
https://www.amazon.co.uk/40x40x20mm-bearing-1-06W-27-5dBA-8000rpm/dp/B07QYWP77Y/ref=sr_1_6?crid=3W0T1WTL787B0&keywords=Sunon+40+x+40+12v+fan&qid=1692862826&sprefix=sunon+40+x+40+12v+fan,aps,155&sr=8-6 and a £10 2 minute timer from Amazon, and connect it to the push button on the Thetford Throne
There are thousands of Sunon fans but what you are looking for is a 12v 2.9W 40 x 40 x 15mm fan. The one included in the Thetford kit is Sunon PSD1204PHB1-A. This will give just the right amount of de-whiffing. I had one on my last van, the official kit, and it worked excellently. I'm getting another van and I will install this fan and a 2 minute timer so that when I press the flush button before opening the slider it will fan for 2 minutes. You can get variable timers, if you think you will need longer - or just push the flush button again briefly which will give another two minute blast.