Using a cheap steel barrel as a jacket?

[tiramisu]

Around here stainless steel barrels are few and far between.
I could probably have something welded up for me
but

55 gallon steel drums are cheap and plentiful.
Is there any practical reason not to use a cut-down 50-gallon barrel to jacket my little beer keg?

Fill up with an appropriate liquid.
Plug in electric elements
Heat up the liquid and let the beer keg do its thing with no scorching and no worry about adding extra water with steam injection.

Anything I'm missing? Rustoleum.