It pays to look in the cull bin at your big box lumberyard. I found some insulation for 70% off, really more because they called it one sheet. So for less than four buck I got ⅔ of the walls insulated.
And if you add the little I had left over from the last trailer ¾’s done..
I wanted to wait until I finished wiring but you have to strike when the bargain is there. I didn’t want to be tripping over it so it was easier just to install it.