More days can be worked in and events can be repeated to accommodate those who show up later. If you are unable to build your own web site for the meeting and keep it updated, people will loose interest really fast. That includes links to information relating to the Summer Meeting site, any travel tips and the like. Pictures would be good to. Gives participants a visual of where they will be.
Location needs to be determined along with the date.
Interesting locations should be considered. A place with Ice Age History or other natural wonder is nice. Clean campground with showers. Good trails for hiking. Nearby cabins or other accomodations for those unable to camp.