Regarding barrel material, I read somewhere that one of the metals wasn't suited for colder climates - could have been s/s, could have been alu. Not sure either way...
I'm not bothered about making the gun a bit heavier - I'm a big lad, so I'm sure I can become accustomed to it. I'd rather be able to dive about than treat the gun with kid gloves.
Regarding paint... not a clue. I know Campaign use (or at least used to use) Blaze paint, but I've since moved and my local site is Delta Force which use unbranded paint, sold in boxes of 2.5k (at £125 per box - ouch!).
Given I use site paint... now what do you recommend