I have taught quite a few watercolor workshops over my career, both indoor and outdoor, and a few in Northern Michigan, as well. Here are some observations:
* Find out when black fly season is in the U.P.--kind of takes the fun out of it, don't you know!
* Make a complete list of supplies to be furnished by participants, such as brushes, paints, papers, supports, etc.
* I usually purchase paints to share to eliminate cheap or crummy paints with all kinds of technical problems.
* Locate and secure permission to use sites that are not public in nature, to avoid angry land owners.
* Each morning have coffee and/or donuts for participants
* Have some kind of warm up painting exercises to get creative juices going and to answer technical questions from the day before.
* Assemble a list of websites, catalog companies and sources for materials, frames, mats, etc.
* Remind participants to bring basic comfort stuff such as sunscreen, a blanket or stool, something for shade, bottled water, etc.
* A lot of participants are older folks, so don't be too far from the "facilities"!
* Only paint during the early hours of the day, because the summer sun is usually tough to take in the afternoon. I usually teach from 9:00-2:00 or less, depending on the heat.
* Your participants will have more fun if you keep things loose and humorous, but you need to keep things organized in your mind, including having a daily routine and a "plan B" for unanticipated problems.
* I usually start the day in the same location, then go out to more remote locations early on, ending the day at the original location.