Lunars did have a reputation for leaks a number of years ago, hence the nickname, "Leaky Lunar". However, there were also "Soggy Swifts" and "Boggy Baileys".
They have generally the same water ingress warranty as most other manufacturers, which is usually six years. Therefore, as with any caravan, make sure that you have a damp test done.
Having said all that, we had a 2009 Lunar Lexon which had damp (under one of the windows and also in the roof), and to say that that caravan was a disaster is an understatement (not just because of the leaks). That has been swapped for a 2010 Lunar Clubman, and so far so good........... You wouldn't think that they came from the same place.
Bottom line is that if you like the caravan and it suits your purpose, it doesn't matter who the manufacturer is. There are good and bad from them all. Just make sure that it is checked properly before you buy.
Nigel.