I’m glad you advise the precaution, I would hope anyone with the ability to complete this repair would obviously feel the same. However, Leaving the exterior side of the specific area being discussed without some kind of impact resistant coating is pretty irresponsible, IME
you may be surprised what is awaiting your discovery, mine looked about the same as yours from the exterior. Have you removed the carpet and taken a look? The tan stuff is seam sealer, on top of primed weld joints. I did apply 3M rubberized undercoating on the exterior side and would again.