As a kid, Dad brought something about like that home, but it was just the frame. He stripped the wood off it and junked that and built it up about like that photo. At the front center he had an extension that stuck up about 6 inches with a 1 1/4 inch + hole drilled in it. The back end had similar. A length of black pipe went through holes just barely and a threaded porch base screwed on at both ends. This established a ridge pole
for the canvas cover. (much like a Wall Tent)
I see the sides of the trailer have the fittings for bungee straps to hold the covering on the trailer. But without a ridge pole the canvas on that trailer would become a pool.
with these screwed onto the pipe at either end on the outside, the pipe couldn't go forward or backward. Worked very well. Inside the Trailer we had plywood boxes as containers so that camp gear was in one, cooking
equipment in another etc.
That was where we started with a Station Wagon before we moved over into Vans.