passive cooling idea for row cover low tunnels

Starting brassica seedlings for fall harvest here is REALLY difficult. The weather in July and August is just too hot, and getting worse.

I start seedlings under row cover low tunnels built of PVC hoops and rebar ground stakes. They are fairly strong and could take a lot of weight.

If I set up a system to trickle water very slowly down the north side of the fabric, would I get significant evaporative cooling inside? Keep in mind that this is Denver, CO with low humidity, lots of wind, and high temperatures, an ideal drying climate.

I'm thinking of either a soaker or drip type hose connected to a garden hose, or a leaky gutter that could be refilled every day.

I would do a propagation mister timer, like in the grocery store veggie aisle.  On for a few seconds every few minutes.  You can find controllers to run an irrigation valve, but it is probably easier to find one to run a pump and just pump from a rain barrel.