well, basically anything that would act like a sealer could be used, i'm sure most of you have seen the red "paint" that is a preventative. I would not recommend using it though, it stains pretty easily and if used in abundance it tends to seep down between the cable end and the post, thus preventing a good connection.  Usually we dont recommend using anything, if things are in proper working order, corrosion is nill... i've seen the felt rings used, but i cant say with any certainty that they work.  Die-electric will work, vaseline, axle grease, maybe even nail polish?... but again, dont let it get between the contacting surfaces of the battery and the cable ends.... (i've seen one or two top post batteries that were literally drowned in the spray on preventive(usually its dark red in color) and the posts were literally covered, preventing contact,  had to take a wire brush to get down to the lead again, guess its almost like a lacquer type paint, doesnt come off easily... ) and someone wondered why this battery didnt work?... ;)