If you try and use that trailer's frame only you will run into trouble as they are built as a box and not strong enough to hold much weight once that box is cut off.
I wouls do all I could to mount that smoker inside and use flat doors for the cook chamber.....it would be really cool!!!!!!
Edit....now that I have looked at it a while here is what I would do.....mount the smoker with the fire box on the front under the feeders in the trailer. Make the whole thing fit inside the trailer and run double flat doors on one side of the trailer for the cook chamber. I would cut the bells off the tank to get more of it inside the trailer and not take up space. The fire box door would be dead center in the front of the trailer. Insulate the firebox and door. You could put a warming chamber on top of the fire box and access it through the front as well. Leave the back doors alone and leave the trailer looking just like a horse trailer.......come on man, do it, do it for me...
![Welder :welder:](./images/smilies/weldersmiley.gif)