I recently had several tanks inspected and "certified". I like smaller tanks as they take up less room, you can set one up at your camp table for a remote burner or BBQ (yeah I know that propane is "pro"fane but it is convenient) and leave one hooked up to your trailer. Also have an aluminum tank that will not rust. It is a visual inspection only and was about $5 or $10 per tank. I also had the valves replaced with OPD valves. I have a good "cost effective" source for valves and they will ship them to you if anyone is interested let me know and I'll dig out my notes. I found that most places won't sell valves to the public. I called the factory to find out what size valve to use as there are several different sizes for different sized tanks (although they all look the same when installed).
Propane testing involves performing specific visual inspections and other tests to recertify the propane tank. Propane tanks are tested differently than most other DOT cylinders. Propane tanks must meet specific requirements visually, and requalifying is a thorough process. Source: http://www.gchtonline.com/Propane.htmHydrostatic Testing is at very high pressures (thousands of pounds per square inch). They pump the tank up, measure how much it blows up like a balloon, release the pressure and measure how much of the expansion is permanent. If the total permanent expansion is less than 10% of the total (as I remember) it passes. If the permanent expansion is less than 5% and the tank has never tested above 5% it gets a "+" after the test date meaning the tank can be filled 10% above the pressure stamped on it.
My tanks were inspected by: Delta Liquid Energy 12685 Foothill Blvd, Sylmar, CA (818) 838-4400.
Horizontal tanks are exempt from OPD valves due to their shape. If they been inspected and certified within the required time frame they are legal to fill and use.
I found this one on Craigslist but it looks a bit big.
http://inlandempire.craigslist.org/for/3167623290.htmlHope this helps.
Cheers,
Gus