Don't know if it helps, but the newest van I've had without a cassette toilet was a 1992 Sprite. The oldest with a cassette was a 1989 Elddis (motorhome) so the answer is that it varies between manufacturers and models, but somewhere between mid 80s and early 90s they became standard.
I bet if you rang Lunar with the identification/chassis number they would be able to tell you the age. It should be on a plate somewhere, either near or on the drawbar or the door.
------------- Caz
If you can't see the light at the end of the tunnel, just keep going till you go round the bend.
we have a 1990 sprite and the previous owners put the cassette toilet in themselves in 2004. Got the original receipts with the paperwork when we bought the van. Lunar may be able to help if you call them with the details of the van they would tell you the age as suggessed by bordercaz.
It does depend on the model as well as the manufacturer - they tended to fit them to the upmarket models first, and sometimes they were an optional extra.
I've just found an advert for a 1989 Ariane (6 berth) that says it has a toilet so this other one is probably earlier than that.
------------- Caz
If you can't see the light at the end of the tunnel, just keep going till you go round the bend.