Do police check storage storage units or bring dogs by?

It depends on the district. The police department I was with did nightly K9 checks of storage premises in high crimes areas. The purpose was to prevent theft and break ins.

Added: HOWEVER - in addition to the building check - if a canine "hits" on a storage unit it would have the same weight as if it "hit" on a vehicle. It would be PC to apply for a warrant to search the unit.