Our contract states the same thing. If coverage is not provided, we will supply a tent and charge $75. Not only does it say that in the contract, I explain it to people when we are discussing an outdoor event. I had it happen last year where they said we'd be under a tent. When my DJ got there, they said there was no threat of rain since it was so sunny, so they moved his spot outside the tent. He called and asked me what he should do. I said they need to pay $75 and set up our tent. They paid. I live in Ohio. Rain is an issue, and so is the sun. The sun can be brutal on my computers and speakers. My electronic equipment simply will NOT be sitting out uncovered from rain or sun. While I've never had my equipment stop, I've heard it happen to others that use the same equipment. It's not just your brand. I believe it's a safe guard built in to good equipment to shut down when it gets too hot rather that just burn up components inside.
I did make a tent exception once this year for a short ceremony, i used a compact and put it under my table for sun coverage, so the amp portion was still not getting any direct sun.