Hi Darren,
Wow, your 'option' list on your Carawagon sounds very comprehensive!
I would think some of those were after-market mods - I can't remember seeing any Searle documentation mentioning air-con or cruise control
What engine does it have now, or are you reconditioning the original?
It would have been interesting to have seen the toilet arrangement (which was a Searle option) - I suspect it would have been a simple bucket with toilet seat and a clip on lid to keep it from splashing when travelling. I remember my parents having an early caravan with just such an arrangement, before the advent of flushing porta-pottis.
As said earlier in this thread, it was possible to purchase a 109" Land Rover and take it to Searle for conversion, which could explain the 251 chassis number.
There may also have been times when Searle could not purchase base vehicles on export chassis numbers - perhaps a quota per year? Or, if a customer was in a hurry, Searle might have purchased a base vehicle from stock, or used a stock vehicle they had in their showroom (they were dealers as well as converters), rather than ordering a new build on an export chassis number.
I hope that helps
By the way, where are you located in Australia?
Cheers,
Robin.