Battery area

So getting ready to put the Bay into winter storage, I found the battery was flat and changed it. On doing so I saw some rust around the battery area which looked like surface rust…but I found two small areas (about 20mmX 10mm each) which if I had poked a screwdriver at would have gone through. I didn’t and put a bit of Krust to stabilise for now. The van is getting an MOT next week - could this be a risk ? I intend getting it sort when it comes out of dry store next year. Is there a way of preventing it ? The van is fully treated underneath so it may have started before the treatment when on…thanks