AbdulAlhazred
Legend
I'd just like to point out that this has been discussed before, and the consensus of veterans who have worn armor and of review of the historical record, sleeping in armor was not only pretty easy, but pretty much necessary while on campaign. For example, Bernal Díaz del Castillo wore his armor pretty much nonstop throughout the entire Spanish Conquest of Mexico. This took several years.
There was even a video posted by an enworlder that owns a suit of plate mail, and he was able to do cartwheels, push ups, climb ladders, and other physical feats that are generally considered impossible by the people who buy the myth that plate made you unable to maneuver easily. His armor was slightly heavier than most historical suits of plate mail.
So don't believe that you need to impose some penalty for wearing heavy armor while you're sleeping out in the wilderness. If you still wish to, you're diverging from real world experience.
Agreed. The general view that for instance "knights could not stand back up in plate armor" or "had to be winched onto their horse" are in fact silly. I've also seen people demonstrate doing all sorts of things in armor, as you say. So in general there isn't a LOT of problem with just wearing your armor.
However it still isn't a second skin. There are times when people would doff their armor and/or wear lighter equipment like an arming vest etc. I doubt Diaz wore his armor when he was lounging around town or whatever. And it is pretty clear that most soldiers in most places and times, even on campaign, often went unarmored.
Finally there IS an environmental aspect to it. Trudging through The Great Desert in your plate armor is going to be rough, just as the crusaders found out. Likewise it might not be so good to wear it 24/7 in a jungle either. So I've always ruled that any penalty for 'sleeping in armor' would be environmentally dependent. Wandering the countryside in a European-like climate? No real problem. In the desert, you might start to suffer some endurance check penalties after a few days.