The trailer is the burley flatbed, back when it came with 20" wheels. Ziptieing the deck to the trailer also allowed me to leave the canvas on the trailer and not damage it if I wanted to restore it back to the original condition . All this wood is 1/2" ply of something I had laying around. If I had your trailer I would try to turn the frame around. My girl almost always was standing.
Good luck with your build. Post some pics of the "after" trailer.