Hi Road Doggie,
Funny you should ask .... I am doing the insulation now. After freezing in southern New Mexico in January at night, I decided to check out the insulation that I had added as an option when I ordered the trailer. They had bubble insulation on the walls, ceiling and floor. The bubble on the walls was just hung with masking tape, and not sealed off at top or bottom. It was one piece all the way around the walls from left rear door to right rear door. One piece on the ceiling and one on the floor.
I am in Las Vegas staying with my niece, so I am able to do the insulation project here. I am adding one inch styrofoam sheets and then will put the bubble over that before I put the plywood back on. That should keep us warm at night next winter, and hold the heat from our little heater. Here are a couple pics for ya.....
Bubble Insulation

Masking Tape ..... lol ...


Starting Insulation Project

Almost cool... warm ....

I am sure you have seen most all will add some kind of insulation. The bubble was not enough for us, so now we will have both one inch and bubble. I would recommend at least the one inch for your trailer. The Haulmark is a great trailer we love it, I bet you will have fun with yours.