I attached the front wall of the trailer first.
I put the plywood on the bottom of the frame since the frame had extra framing supports welded on the sides
I connected the right wall next. I only painted the inside of the trailer so I could attach to the frame and not have to worry about taping walls up and making a mess. I realized when already assembled that I should have painted all four sides of the framing. I only painted the 3 sides you can see.
With the one side fully up......
Looking at the back...
You may call me crazy or stupid but I used a 1 inch paint brush to paint this whole trailer. I have my reasons tho. Bigger brushes results in more paint lost in the bristles. Using a paint roller puts a thin coat of paint and although it is quicker, I would rather take my time and save money by using less paint. In all I used a gallon of gloss black, 2 pints of brown, and 3 gallons of gray.