Old propane tanks in Class B RV - how to change out?

[thedanimal]

Hello,

I aquired a 1971 Ford E300 Shasta camper in great shape however the horizontal propane tanks are from the 80's so I need to change them out. My question is, can I replace these with standard #20 pound tanks? I searched for horizontal #20 tanks on Ebay and they are upwards of $400 per cylinder!? If I cannot fasten them in should I just remove the old ones and buy the extension kit and run a standard #20 in the vertical position? Any reason why I would not want to give away the original tanks? Thanks for any help on this!

[thedanimal]

They look fine, however I was "informed" that (at least in Colorado) tanks older than 12 years need to be replaced and was under that assumption.

I just read that if they don't have an overfill prevention device they need to be replaced. Is there a way to tell if they do from the exterior? Or perhaps new fittings include this?

[rvten]

Why do they need to be changed out?
Valves gauges and fitting can be replaced on them.
Tanks can be sanded and repainted.

Is there a problem with them you did not mention?