This is how I mounted a Wave 3 in our old ranger II, not a Hawk but perhaps this can add some ideas.
I originally mounted the heater on three screws hooking to the factory mount holes on the back of the unit.
After using the Wave 3 on a few trips and discovering firsthand how directional the heat is, I at least wanted the option of pointing it toward my seat and more into the living area. I figured a hinge would work.
I took the unit completely apart so I could drill and mount the length of piano hinge and docking latch to the back case. Because of the grills over the furnace outlets and outward position of the mounting holes, I used two pieces of 1/8” aluminum as a spacer under the hinge. I used a piece of aluminum for the latch arrangement and a brace to hold the heater in the outward position. I installed a ¼ X 20 threaded insert in the cabinet and use a bolt to hold the heater in place for travel.
When in the outward position I use the same bolt to hold the anchor brace in place via a hole drilled in the top of the heater case.
I used pieces of adhesive fuzzy (loop) Velcro as cushions on the back of the heater case and also along the bottom of the anchor brace so it fits snug in the space between the heater and the bottom of the cabinet edge. Although the grill of the Wave 3 gets very hot, I have found that the back case gets only warm to the touch.
Borrowing on Lighthawk's installation, I also used a length of rubber propane line and a quick disconnect. I tapped into my propane supply lines with a tee at the factory furnace connection. I had to pull out the furnace to access the supply line. This was the hardest part of the install.