Need Mattress measurements 2003 Star Craft 21rb

How much is it to buy the split replacement cover from Starcraft? I would buy just the cover and then find someone local to buy the foam inserts from. I wouldn't be happy moving a one piece mattress into the aisle everytime I was putting up the camper....the mattresses are tucked up nice on the ends when folded and if we are on the road sometimes we stop and cook lunch inside and moving around with a big mattress in the aisle wouldnt' be fun....