Sealing sheet metal

Hello Everyone!

Some of the talk on this thread about sealing metal got me wondering.
I purchased some 1/4 in thick sheet metal for a small welding project
and was wondering how I could seal the metal to protect it against
corrosion. The projects are a mirror and picture frame so they
shouldn’t be items left outside, but I know that over time,
everything corrodes…

Any suggestions for sealers? Would a sealer even do the job?
Thoughts welcome.