Never thought of this till I read it here. But I can see it being a real issue, and even more so in an emergency. I would think some type of vibrator (lets be nice here!) in the mattress that would go off if hooked to a smoke/fire/CO/LP detector would wake you. good luck with the trip, but I would seriously consider a second person to go with you or another RV`er so you could have to vehicles in an emergency or a breakdown.
I cant wait till I can do that trip.
Edit, I found this
Safeawake. seems like something like this would work, I`m sure their are more out there.