Hi, I was looking into an emergency air supply like Spare Air. I'm an armored car driver and I'm slightly concerned that if the car goes into the drink I won't be able to get out. I can't go into great details about escape procedures but it's not hard to imagine that if it's hard to get into, it's also hard to get out of. Not to mention the fact they're extremely heavy and wouldn't float well. So what can you suggest? I've seen a 1.7cf spare air for about $200 and a 3cf spare air for $250. Are there any other options? Would you buy new or used? Thanks!