Timothy, In my opinion it wouldn't matter. Other than current rust, having had a steel body should not matter. If there is no current rust, it should be fine going forward. I wouldn't worry about the relative weight, as the weight savings that will come from jettisoning the propane stuff is huge!! More if you remove the some of the regulatory stuff like the high bumpers with shock absorbers, etc. All this will easily eclipse the added weight of the steel.
Cheers,
