I would guess that this is illegal, and you may want to find a hatchery to buy some from instead. At the very least if the DNR finds that you have browns in your pond you would have a recite to explain where "all of them" came from.
If you happened to find a brown trout hitch hiking his way across Iowa I would get a cooler, bigger is better, and maybe a little ice, You don't want to temp shock them. I have heard that ice oxygenates water as it melts. Also you could get some "stress reliever" or decholorinator at a pet shop. They generaly help fish stay healthy, absorb ammonia, and remove toxins from the water.
Make sure you slowly acclimate the fish to the pond water. It will most likely have different PH, harness, temp and every thing else.
