Can you install pro flex in un-heated areas?

Unheated doesn't matter, it's plumbed through attics here in Texas all the time - check the suppliers website, but I can't imagine it'd be a problem. For long runs, you can get this readily in 25' and 75' - but you can also order a spool of 200' I believe, and then you don't have to worry about unions to potentially leak inside a wall cavity somewhere. One thing I like about this stuff is there aren't 12 different tees and elbows to leak, just one fitting at each end.

This pipe is designed for many applications. If run in walls the primary requirement is that it cannot be exposed to normal activities. Such as someone putting up picture hangers or such. This pipe is plastic so wherever it is applied in a hidden environment it has to be protected or shielded. Also when going long distances use longer pipe as you do not want several joints which could lead to leaks. Use pipe clamps wherever possible. Just make sure the pipe in the attic is not in an area where it can be damaged.