My $00.0002
You might want to have a little come to Jesus with the company who make the tanks you may purchase.
A 3000 psi bottle at sea level will not have the same pressure characteristics as at altitude when cold.
You need purpose built tanks with guarantees that the manufacture will warrant the tank from catastrophic failures at the maximum target altitude and lowest/highest temperature.
If I sound a bit to concerned, it's because for the last 13 years I have worked at a dive shop. We were very fortunate and had no catastrophic tank failures.
There have been failures in the Keys and we were intimately aware of the effects and consequences. People die from being lackadaisical and inattentive.
The USA Tags & Bags about 150 SCUBA Divers per year. Florida is at the top of the list most years.
Fortunately, I think it's been about 6 years sense the last tank accident.
This guy only lost his arm
http://www.youtube.com/watch?v=9lw_fhNAIQc
Be safe, very safe..