since you will never be connected to the internet, why not just use whatever address space comes to mind? oh, you're worried about collisions? with whom? you said you were not connecting to the internet.
As I have in the past been involved in a couple of such requests in the past I can add the arguments as I remember they were used then: - we are going to connect to networks who are connected to other networks and some of them may be connected to the inthernet - thus the need for globaly unique adresses - we may at some future point be connected to the internet.
yep. expected. so please go to your nearest rir and get real address space.
Maybe its better to ask are you prepared to renumber your network when you connect to another network ?
the answer to that will always be "yes" as you did not scope 'when' randy