Constipated Toddler on the Road

We are on day 4 of our trip and DD is constipated. We are on a 3 week trip to the west and southwest. I think she is backed up because of riding in the car so long. Yesterday and today we have made several "potty" stops for DD. She really needs to be able to stand to go potty especially if she needs to poop. We are in our truck/camper combo. Truck has a back seat for DDs carseat. It obvious she really needs to poo poo. This morning, because I knew she need some relief soon, I gave her a liquid suppository during her diaper change. When we stop and letting her run around, she walks around until she obviously feels the urge to poop and then stops and gets into "the position". The position is a standing half squat with legs slightly spread. She pushes, turns red, and grunts for while. Then she starts walking around until she needs to try to go again. Poor thing is trying so hard to go. I am making sure she constantly has a sippy cup of water or watered down juice. She had two prunes at lunch. I think when we get stopped for the night she is gonna need some bare bottom time if she can't do her business while we travel. We did that last night and she tried to poo poo for quite awhile before she got tired and fell asleep. I know she is must miserable.