adding substantial mass to the thin metal panels will help, especially with 100%+ coverage.
you don't get true damping, and it smells, but it will be better than nothing.
i've used the asphalt based sheets that parts express used to sell in some previous cars (8+ years ago). put a large sheet on each front door - covered the entire door. it did the job of a noise barrier but didn't stick for shyt.
if you want to lower road noise, you could use peel-n-seal, but best to put foam or carpet padding between it and the metal so it acts as a barrier. MLV is the superior option for this though.