It's just so hard to explain to folk who drive a 1/2 ton truck how far short those trucks fail under extreme conditions. And a 13 mph side wind is not even extreme.
In your situation, you did the right thing. You slowed down and made all attempts to get out of the wind. And yes, I'm so sorry to say this, but size of truck does make a difference. A 30 foot trailer is a bit much for a 1/2 ton truck.
My personal advise and my original coined quote:
“You really need to think in terms of what is the ultimate extreme usage you'll be experiencing with your truck, not what is the lightest usage and hope it's OK when the extreme happens."