You could also carry 1 extra 20lb tank for just such a need. Instead of replacing the 33's, use a 20 and a 33, and replace the 20 as needed.
I don't know, there are many ways to do it. Years ago, on our Salem TT, we had 2 - 20's since new. I added a third to storage, and could rotate out as needed. Different, but just a thought.