How would it be delivered or picked up? Dumped on your floor? Pallet boxes? Dumped into your pickup box with a front-end loader?
Agrostis is right. After a few days of high humidity--it will probably absorb moisture and become hard as bricks.
Do you plan to spread it or dissolve in water? How are you going to measure it so you get 150 pounds per tank--or whatever your mixture calls for?
Perhaps best to have the urea elevated to a big plastic tank on the second floor. Open a valve onto a bucket on a scales to weigh the correct amount. Then tip the bucket into your tank and add water. Truck must drive under the bucket.
Good filters inside the tank are important...as is the ability to clean out the trash periodically.