
Hi Sean! Welcome to BYH from the big, beautiful state of Texas!
You came to the right place for advice. You have some great neighbors there in Northern California. As a kid I lived in Fresno and then moved to San Jose. It's been more decades than I care to admit.

But I still remember the fog! UGH!
We have a 10×17' canvas garage, that we got from Harbor Freight. After reading lots of reviews, we took some of their advise & used self tapping screws to hold the metal tubes, in the framework together. We also used anchors, to hold it down & have had no problems with it blowing apart when we have occasional 50-60 mph winds.
Here is the garage right after we put it up
We have been storing our hay in it since a year ago last August & it has stayed nice & dry. We put cinder blocks on the dirt & then put pallets or some kind of lumber on the cinder blocks. That allows for air circulation under the hay. There is some air flow under the canvas walls. But, we also unzip & roll up the door, on sunny days, so there is plenty of air flow.
we just bought 30 bales . . . (approx. 60-70 lb each) of chemical free coastal hay.
We still had 17 smaller bales left over from last year. We pulled them out & stacked them, and they will go back in, now that the newer hay is stacked, so they can be used first.
We covered the stack of old hay with a tarp, because we were expecting rain. We did get 3/4" of rain, so were glad we covered it. Now the tarp is off, so it can air out before we restack it.