Question about mileage and deducations related to storage unit

Hello, I'm hoping someone has some insight for me! I work as a 1099 subcontractor installing residential real estate signs. In the past year, the housing market has gotten really hot here, and I have a lot of posts and panels in inventory. I'm thinking about renting a storage unit to keep everything tidy, instead of having my front yard look like a post factory! If I do so, can I write off the cost of the unit's rental? Also, when logging my mileage, I would of course go to the unit first to pick up whatever posts and panels I need for the day's work -- would this be considered my first stop? (I don't want to log my miles this way and then have them disallowed.) Thanks for any insight you can provide!