When I cut my plywood pieces for my side walls, interior and exterior, I made a cardboard template. I then transferred this to the plywood (5mm) for the basic shape. I set a few finishing nails and then took a couple of sticks of thin cedar I had stripped and created the curves that both fit the basic design I wanted and worked well for the cedar. I drew this out on the main boards, it takes 3 pieces to do mine as it is 5x10. I then clamped all 4 piece of each of the 3 sections together and cut all 4 at the same time. Thus, 3 cuts gave me the semi-finished cuts for all 4 sides of both walls.
Once I finished laminating my framing members and foam to the plywood all I had to do was take my trim router and bring the frame down to the actual size of the plywood that was cut. When all done (and this really surprised me) there was not one area of either wall that was off by a 1/16 inch over the opposite wall. I use everything I do to one wall and mirror it for the other wall. It is how I just did my cedar strips for the exterior finish.
So, in a nutshell, if you create 1 template you can fairly easily copy this to both sides by cutting them both at the same time. Whatever that template is, that is what you get and having identical sides will make the finishing part easier.
And by the way, I am a complete and total rookie at building tiny travel trailers, but I just look at them as little sailboats.
dave