You’re invited to a state park early next month, for work or play.Iowans alone or with kids can put in some public service helping paint picnic tables, pick up litter or do other improvement projects at state parks. Friday May tenth through Sunday the 12th, many parks are holding cleanup days and will be happy to hand off chores to volunteers who show up. And 53 state campgrounds that same weekend will welcome campers free. The weather isn’t guaranteed that early in the season, but state officials say three days of free camping is their way of enticing more Iowans to camp, swim, fish, boat and hike the state parks more often this summer.