Obtaining Propane Tanks

[SJSVOB@aol.com]

Here's a transcript of my first phone conversation trying to obtain pricing 
on a propane tank for a psub.  (I know, I know, I shouldn't use a Propane 
tank and I should follow Kittredge's design, I know better now, but here's 
the conversation anyway)

AGENT: Hello, XYZ Propane Tanks, How may I help you?
ME: Yes I'm interested in a propane tank, about x ft by y ft.
AGENT: How much pressure does it need to be rated to?
ME: Hmm, well I'm not really sure,  do they come in different ratings?
AGENT: Well what are you going to be using this propane tank for?
ME: Ummm, well....actually I was planning on making a submersible vehicle 
with it.
AGENT: {LONG LONG PAUSE}.....you wanna do what?
ME:  Well I plan to make it into a submarine.
AGENT: {LONG PAUSE}  no.....{sounds confused}....you can't.....no....you just 
can't make a submarine out of a propane tank sonny.
ME: Well sure you can.
AGENT: Aint' no way you can make a submarine out of a propane tank.
ME: Well people have done it before.
AGENT: Who?
ME: (list names of people I saw on the internet that did this)
AGENT: no....no....you just can't do it....besides you'd never get it rated.
ME: Well I don't need to get it rated as it is just for personal use.
AGENT: {LONG PAUSE, THEN VERY QUICKLY}  You mean to tell me you plan to put 
your friends and family in it and sink it under water?
ME: {PAUSE}  Oh yeah sure.  It'll be a hoot!  My 2 month old and Labrador 
will love it!  {Ok at this point I'm messing with him}
AGENT: {PAUSE AGAIN} alright, an x ft by y ft propane tank will run you z 
dollars.
ME: Well what providence!  I have enough in my checking account to cover it!
AGENT: CLICK!

So does anyone have any tips on obtaining a pressure hull?  Does anyone know 
of someone to contact that won't be totally wigged out by someone wanting to 
make a submarine?

Steve