RockyMtnRay installed a side A/C in his TM. I don't know if you can access this page, but here is the link:
http://trailmanorowners.com/forum/sh...highlight=side
It would probably be best to have a dealer do this for you unless you're really handy. You would probably have to cut out the drawers installed there (if there are drawers), install a drip pan and a drip hose, and add an electrical outlet to power it. You would also have to cut a hole in the outside wall and add a vent screen. Then you would have to secure it to the TM with a strap and frame it in so it looked good.
We used to have a side A/C, located to the immediate right of the oven in the space right below the counter. It died, and we took it out; we don't camp where it's hot so found no need for it, but have left the space open. When we're camping with hookups we use the space for a microwave; without hookups we leave the microwave at home and put drawers in the space. I kept the drip pan and hose, and sealed off the outside vent with a contact-covered piece of foam board. I moved the outlet, but it's still there for use in case we should ever want to replace the A/C.
You might call a nearby dealer and ask them what it would cost to add either side or roof A/C.