Propane tanks 10 years old, what is best choice ???

I live on the salt water, and I'm lucky to get 6-7 years on my 20# propane tanks (for my BBQ). I take them to get refilled and they often say: This will be the last time. Rust is the enemy. I've found that it is cheaper to exchange the tanks than to get them re-filled and re-certified. Life is too short to remove the rust and repaint.

Besides the fixed propane tank in the MH, I carry (2) 1 gallon tanks for the BBQ, fire-pit, etc., and they do not seem to have a problem with rust?