Your catalytic looks like would put out some Btu's but does it burn the ankles? The easiest and cheapest is an UN-vented propane heater, I'm thinking on running a supply hose in and mount a small round infrared heater that are so common, maybe on top of the tall cabinet with the mirror? Venting would be through cracked window as suggested or cracked roof vent. The low oxygen shutoff feature or a battery powered carbon monoxide sensor sounds like a must. Excuse my ignorance but does carbon monoxide replace oxygen as it is used up.
Yes, it does get a bit warm if you get too close to the heater. However, I use this feature to advantage. At night, I hang my damp socks opposite the heater and they are dry and toasty in the morning.
Positioning the heater in a high position will leave the floor cold as heat rises.
The carbon monoxide is a byproduct of the propane consuming the oxygen. Another byproduct of the combustion process is water. Cracking the windows will vent most of this moisture. That said, you will still get condensation on the metal parts of the window due to the temperature differential between the interior and exterior temperatures. Be sure to cover the small forward window in the lower unit as the condensation on the metal frame will soak a sleeping bag over night. Been there, done that. I cut a piece of door skin (1/8" plywood), stuck velcro to it and the window frame to hold it in place. End of problem.
Finally, as I previously posted, install a battery powered CO detector and check it before you leave the driveway.
Mike