Mine is under a tarp for the first time this year.
I also had 2 bundles of cross ties and I made rows for the hay to sit on, I put the ties end to end with a gap between of 2 feet and they are on 3 foot centers. I can come in from either end and pick up or drop a bale of hay. I have rows long enough to put 10 bales and my tarp covers 3 rows (30 rolls and it cost me $55.00 and it will probally last 4 years if you put it up when not in use.
I figure if you save 10% of the hay each year by covering it, the savings will cover the tarp and cross ties.
JMO for what it's worth.