a. Propane and ethanol create similar ratios of heat to water vapor. High school chemistry, count the moles.
b. Propane detectors alert to any flammable gas. That is what they are based on.
c. Any unvented heater produces and unhealthy level of carbon dioxide in less than an hour in a small, ventilated space. OSHA limits CO2 to 5000 ppm, but 1500 ppm is consider the limit for investigation in homes.
d. Refilling is not really a problem, for me. I don't turn the heater on until dark, at which time I fill the tank. It will last until 10-11, at which time I turn in and crawl into a thick sleeping bag. I would not leave ANY simple heater running at night. But NEVER refill a hot stove. I also prefer to remove the can and put it on a lipped tray on the counter to refill; in that way I can see what I am doing and spills are contained. Easy.
Really, the most you should run an un-vented heater is cooking a meal, and not a really long one. Carbon monoxide is NOT the only hazard. Oxygen depletion is another issue. Mostly, you may just feel muddled an loggy.
Unfortunately, there is no such things as a simple vented heater on the market. I've designed a simple vented stove top heater that can be put together for lunch money in an hour. It will be in a magazine, but it's not hard to figure out; just look at the Sig Cozy Cabin and see how little there is to it, other than the burner. No fan, no thermostat, no sealed air intake, just a can and a vent. The key is that the exhaust must go outside.Every portable heater has a warning about leaving a window cracked, but there goes your heat, and how much do you crack it? Makes no sense unless you live in a barn.
[I had a fancy sealed heater on my cruising cat. Very nice for the 4-season cruising I was doing. But my F-24 suggested something much simpler.]