I tried it last year. I bought a 2 perso coleman tent. I bought 2 bbqs that you get out the supermarket. I'd wrote notes and had made a advanced directive (can't remember if that's what it's called) and put it in a poly pocket outside the tent. I remember it was raining.
In the end I thought one would end me after reading about so many accedential poisonings. I lit the bbq and waited 30/35 mins till coals were white/greyish and no smoke. I placed it in tent. I took a 5mg diazepam and had some Jack d, I went and posted letter to cpn. Came back, went in tent around 25 mins later. Fell asleep.
I woke up some hours later freezing (it was in January) and spewing, there was a hole in tent and the duct tape was half off air pockets/vents. I had a great headache and was dizzy, I panicked and pressed the emergency button on my phone. Ambulance guy arrived at my tent, he was such a bastard until we got in the ambulance. The police and firebridgade (spelling) came. A policeman came in the ambulance with me and they sat with me over night while I was in hospital. I had oxygen in the ambulance and in the hospital. I mind the police guy asking if he'd (the ambulance guy) ever seen those numbers before and the dude answered "no" but dunno what they were talking about. I also lost my voice, it came back few says later.
What I learned
Use 2 barbecues
Put on bricks or buy container for bbqs
Use something stronger for duct tape