Savage Wombat
Hero
When I was considering similar rules, I used a Survival check instead of a saving throw. Seems more thematically appropriate. But you wouldn't want the DC too harsh in that case - you don't want to make a skill feel "mandatory".
I ran my Dark Sun campaign in this mode for a while. It was fun initially because it emphasized how different and dangerous Athas was but eventually I stopped using it for regular play because in a normal session, the PCs have the gear and provisions they need to survive, and without time pressure the PCs would be able to practice their desertcraft just fine. Rolling dice for it was redundant.
I kept the rules in reserve though, just in case they ever got caught out without gear.
Sleeping in rigid armour is pretty hard, since you'll often wake yourself up when you change position as you do naturally when asleep. However most suits of metal armour will incorporate what is to all intents and purposes a suit of padded armour, which will be fine to sleep in.
The hygiene and olfactory issues caused by wearing the same gambeson for three weeks running without taking it off are another matter. Probably one best not covered by the rules though.
For my table, it has only been a problem when the players like to say they wear their armor every day of their life 24/7. I literally had a player who was woken up in the middle of the night in his castle while he was sleeping in the same bed as his wife and was insistent that he would be wearing his armor.
For the most part, I'm willing to let a player try to rest while in a dangerous area with their armor on. If they start insisting that they will wear the armor when they have a comfy bed to sleep in, I would consider penalties.
Basically when every day, or even every hour, of travel counts in the story, then those checks become meaningful. I only have them make checks when failure has real consequences to their story.
I am only having them make checks every hour if they don't have cold weather gear on. In other words, it's if they were caught out in the arctic with only a t-shirt on. They will slowly freeze to death.There is another elephant in the room that you shall consider, concerning not how the checks are determined, but their frequency. In situations of extreme cold or extreme heat, for example, you have players making checks every hour. Were they to travel half a day (a typical "montage" for traveling purposes, you would be asking them to literally 4 or 5 dice (potentially more if it is an entire day of traveling) that are the same exact check with maybe a slight increase in DC as the hours linger on. In an hour by hour approach this type of check is fine, but in longer situations this WILL slow down the game substantially.
For example, when I ran a Reign of Winter game awhile back for the pathfinder system, this was a large source of annoyance for both my part and the players, and failed horrendously at capturing the feel of "hardcore wilderness" feel we were going for in the first place. All it really accomplished was bogging down the game and making "unfun" for all of us. Now, obviously, this was all different system (one in which fiddly bits are more welcome, and which I did have), but the principles of much of it still applies.
One thing I would consider doing for the sake of game flow (all what I indeed did for the above campaign) is to have the players make one check and base the hours traveled on the lowest die roll (i.e. the "weak link" in each case). I would then tell them how many hours had passed and that that player had then gained a rank of exhaustion, giving them the option to then rest or use magic to reduce it, or press on, reroll, and likely have that exhausted player slow them down. Once they travel 8 hours, they typically will rest anyway, unless they are in a hurry, in which marching rules come into effect. For the other system game, this caused them to still feel the effects of the cold/heat, as it caused them to go less distance each day (or risk a player being seriously crippled), but kept the game moving without rolling a bunch of unneeded dice.
I like your general thinking. I'd probably simplify this to a single roll for sleeping in armour a few nights running. And I'd cap it at a maximum of one level of fatigue (that can still stack with levels from other sources).Sleeping: A character cannot easily sleep outdoors in armor and get a good night’s rest. Sleeping outdoors in cloth or no armor requires a DC 5 con saving throw. light armor requires a DC 10 con saving throw. Medium armor requires a DC 12 con saving throw. Heavy armor requires a DC 15 con saving throw. Failing the save results in a fitful night and waking up with a level of exhaustion. A tent or some kind of shelter from the elements gives you a +2 to the saving throw. A bedroll gives you a +3 to the saving throw.
Every hour feels too frequent. Rather than making checks every hour I might suggest making a single check every 8 hours. Less granular but the odds can be worked out to amount to the same thing.Extreme Cold: Surviving in extremely cold or hot places, like arctic or desert climates, can be a challenge. If you are in an arctic climate and have no cold-weather gear on, you are going to slowly freeze to death. You must succeed on a DC 10 Con saving throw each hour or suffer a level of exhaustion. At nighttime it becomes a DC 15 Con saving throw every hour. If you have cold weather gear on (thick coat, gloves, boots, head covering), then you automatically succeed on the saving throw during the daytime. But at nighttime, you make a single DC 15 Con saving throw for the whole night if you don’t have shelter. If you do have shelter (a tent, or using your survival skill to make a snow shelter), it becomes a DC 10 Con saving throw. If you can make a campfire near where you are sleeping, you get a +3 to the saving throw. And of course if you can use magic to keep yourself and your co-adventurers warm, you can bypass the problem.
I'd probably tie this to a short or long rest rather than to 4 hours.You can decrease your exhaustion level from the cold by one level for every 4 hours you spend completely warmed by being out of the elements or warmed through magical means.
Same as above, I feel like this could be fewer checks at a higher DC.Extreme Heat: If you are in an extremely hot place, like a desert, you will need to consume twice the amount of water that you normally require. If you don’t have access to drinkable water, you must make a DC 5 Con saving throw for the first hour, or suffer a level of exhaustion. The DC increases by 1 every additional hour. Characters who are wearing medium or heavy armor have disadvantage on the roll. Characters who have drinkable water but are wearing medium or heavy armor must still make a DC 5 Con saving throw, increasing by 1 every hour, but they don’t have to make it with disadvantage if they have sufficient water. If you only have half the needed water, you start making saving throws after four hours of being in the heat.