Why no CO? Its really very "safe" if you have your own space and a bit of money. A relatively cheap tent like this
can be sufficient, though I would recommend duct taping the seams and zipper once inside.a bag of charcoal is usually about 20 bucks, A chimney starter
is 15 bucks and some cinderblock to rest the chimney inside is cheap as free if you can find some, or from a store
is cheap. I would personally recommend one of these
on bottom, then the chimney on top of that, with some regular cinder blocks around it. The goal is sleep then suffocation due to not enough air on the brain. Not burning to death along with anyone near you. start up the chimney (a single match to some ripped off chunks of the bag the coal came in, shoved under the chimney), wait 20 minutes till the coals are white, while waiting, start duct taping the inside and maybe outside of your tent along the seams. wait for the zipper. when coals are white, take them inside. Zip up. go to sleep. Id imagine this part is way easier if you take a small handful of sleeping pills right as you start this process and maybe some melatonin. Just dont stop moving till you are zipped up ready to sleep next to your homemade fireplace.
There is always a short drive to a cliff, most places have them (sorry midwest in the USA).