Tamra,
Can't say what the original shelves were, now that the boat is over 40, buy mine were made out of acrylic sheeting with holes cut for ventilation. In my opinion, it was a horrible design, as the ledges (shelf supports) were placed such that you could never store anything much taller than a jar of pickles or jelly. Not my typical dinner. I have addressed this in an older thread (Ice Box Liner Removal) that offers a suggestion for a much better solution. After viewing the post, scroll down a bit, and find a second post on the same thread... I've made an update to this one in response to your question.
I hope this helps.
Jack Webb - http://HighSeasDrifter.net