I've heard a few things re: soda bottles, but the bottom line is they work just fine. Thoughts on them are:
- Caps can be re-used once or twice before they start to lose their grip. Not necessary to replace the caps each and every time though.
- Avoid the root beer ones (kinda like kegging, eh?!)
- Oxy clean for 30 mins, rinse well, then Star San should take about any odors out
- Keep them in a brown paper bag, well closed. Avoid teh skunk.
So with that, I say give it a shot! Plus, if it's a porter, you could even leave the Cola label on the bottle - like you said, stealth factor!
I've actually thought about trying plastic bottles for shipping in swaps. I want to run a few home tests on durability / long term viability. But the lessened weight and increased resistance to breakage seem appealing! (Like Yuri's aluminum bottles he used.)