Rubbermaid Baby Changing Station I Am Making A Kids Wagon Into A Jeep. What Would Be A Durable Yet Light Material To Mold The Body With?

I am making a kids wagon into a jeep. What would be a durable yet light material to mold the body with? - rubbermaid baby changing station

There is a basket with a garden. Made by Rubbermaid, and I repeat my Jeep Wrangler for my baby to withdraw them. If the mold of Bondo in a draft?