How do i get rid of rust bubbles on my vw beetle?

my vw beetle has rust bubbles on the roof of the car and some are blistered and some are opened they are about 1cm diameter and other ones are much smaller. how do i get rid of them?How do i get rid of rust bubbles on my vw beetle?Sand them down until they are level with the sheet metal. Fill them in with fiberglass. Sand again until level with the sheet metal. Prime then paint.How do i get rid of rust bubbles on my vw beetle?first you must find the cause then it can be corrected there has to be moisture somewhere eliminate the moisture and the bubbles will stop forming then you can sand and prime and paint How do i get rid of rust bubbles on my vw beetle?sand paper and a rust resistent priner