How are you getting your bags to LaMars? Drop them off at the main camp instead of the hotel. Set up one tent at the main campground on Saturday and put other bags in the tent overnight. Backpack your overnight needs for the hotel. Return on bike with backpacks Sunday morning. Take down tent and load bags on truck.
Alternatively, become real good friends with another team with vehicle at the hotel in LeMars and you might be able to have them drop your bags at the luggage truck in Sac City on Sunday afternoon.