I'm not real sure what an 83 Scamp
interior is like but I'm guessing it's much like our 97. The interior cabinets are fiberglass with a white jell coat. The partition wall interior for the bath and the inside of the hanging closet had yellowed. I painted the partitions with Interlux perfection which is a high dollar, 2 part and self leveling marine paint. It runs about $65 a quart but is the next best thing to jell-coat.
If your cabinet gel coat is not cracked or damaged, you can just buff it out with a buffing compound for fiberglass. Maguire and a few others offer kits to remove oxidation and renew fiberglass jell coat. You might want to renew your outer fiberglass skin as the 3 bottle kit would probably do both the cabinets and the outer skin.