Toppers not protectors. The uni normally supplies a mattress protector to keep the mattresses clean.
@FingernailNibbler, contracts are usually for 40 odd weeks to include Christmas and Easter breaks, so they can leave most stuff in their rooms. DS1 had a 34 week contact in first year at Warwick, so could leave stuff at Christmas but not Easter. I fetched his mattress topper home a week early and apparently he had a horrible week’s sleep without it!
I’d check the uni accommodation pages, the length of the contracts are usually specified.