Tenants storing items -- free for good faith? charge?

[Ryan Logue]

Excellent rental on a private college campus within a large city. Rent is $3000/mo for a 5 BR house (comp rents away from campus are $1500/mo).  This is the type of house where 5 unrelated college students rent the property together. The yearly group of students that historically rent this house are from an excellent, academically minded, "calm" fraternity. I'd love to keep the good will with this revolving group as they pass down the house to future generations. I am fearful of other frats / sports teams etc that are flat out animals (we've all seen the movie). 

Due to Covid, current lease dates were signed a bit off-cycle compared to what is common for this campus. Here is our scenario... The current lease with five student tenants ends 05/15/2021. Three of these tenants will be returning to start on the 06/01/21 to 05/31/22 lease between five tenants (ie 3 carryover, 2 new). The three tenants that are on both leases have asked to store their property in the rental during the non-leased time from 05/16 to 05/31, as they plan to return home for a brief post-semester break.

At minimum, I will addend either the current least out to 05/31/21 OR addend the upcoming lease to start early on 05/16/21, it would just depend on which group (current v future) will sign the addendum. All will be required renter insurance, carry the utilities. 

Would you charge extra for this scenario?  Full pro-rated rent? Nominal storage fee?  I'd love to keep the good will with this group. 

Half month rent is $1500.  Storage facilities 10x10 charge $40 + renting a truck to move $30 + time/labor to move items.  I get it -- I'm the landlord, I'm the boss, don't let tenants push you around, ya ya. 

What would you charge?