Many of us here hike kilted Blackrose, though I have never done so in the rain. I understand the biggest concern is ensuring you wear your kilt high enough so that it doesn't rub on the back of your knees. Apparently that is a much greater problem when the kilt (and or your skin) is wet then when dry.

I typically only hike in trousers if it is very cold, or am in a pest infested area. Being in California, it is pretty easy to avoid both with a little planning, and I typically bring lightweight hiking trousers just in case.

Have fun!