Neonchameleon
Legend
With all due respect, and to emphasise what others have said, having to roll against a disease every time you open a door sounds as annoying as 


. It's five rolls (one each) just to open one damn door. Something that they have to do anyway. It's not something they can adapt their tactics to. It's not something that will make them either more or less cautious. It therefore won't change their playstyle. Just make them roll lots of annoying dice.
If you want to make things worrying for PCs to open doors, make each door radiate necrotic energy. 5 points of necrotic damage for trying to open it either normally or for a thievery or strength check to open it if they are standing next to the door when they try. If they mage hand to turn the door handle, good for them. The castle's scary and they shouldn't be there - but they've learned to manage some of the dangers. This way the PCs can mitigate the risk, they can control who takes the damage - but the danger is always there. So it adds to the spice rather than subtracts.
Or if you must go with disease, either short rests or extended rests. Penalising the PCs for taking a rest rather than opening a door works - it tells the PCs that they don't want to stay in Castle Ravenloft because the longer they stay the worse things will get. If you're doing this, give the PCs chains of trivial fights - the sort you don't actually need to take a short rest after. Do they push on without catching their breath in an effort to get through the castle faster (and take less risk from the disease) or do they proceed more slowly, rest and patch their wounds, and take the ravages of the disease? Again, the power is in their hands but the point that this is not a good place to spend time in is made. ... Now I come to think of it, this is a better idea than the necrotic doors.
Also don't penalise the PCs for being trained in endurance. I'd go with that for the disease and will for everything else (including IIRC resisting the negative effects of the Moon Madness).




If you want to make things worrying for PCs to open doors, make each door radiate necrotic energy. 5 points of necrotic damage for trying to open it either normally or for a thievery or strength check to open it if they are standing next to the door when they try. If they mage hand to turn the door handle, good for them. The castle's scary and they shouldn't be there - but they've learned to manage some of the dangers. This way the PCs can mitigate the risk, they can control who takes the damage - but the danger is always there. So it adds to the spice rather than subtracts.
Or if you must go with disease, either short rests or extended rests. Penalising the PCs for taking a rest rather than opening a door works - it tells the PCs that they don't want to stay in Castle Ravenloft because the longer they stay the worse things will get. If you're doing this, give the PCs chains of trivial fights - the sort you don't actually need to take a short rest after. Do they push on without catching their breath in an effort to get through the castle faster (and take less risk from the disease) or do they proceed more slowly, rest and patch their wounds, and take the ravages of the disease? Again, the power is in their hands but the point that this is not a good place to spend time in is made. ... Now I come to think of it, this is a better idea than the necrotic doors.
Also don't penalise the PCs for being trained in endurance. I'd go with that for the disease and will for everything else (including IIRC resisting the negative effects of the Moon Madness).