I don't recall specifically stated rules about sleeping in Armor. But having worn both Leather and plate armor can tell you, Well fitted armor is Comfortable, but sleeping in it would be problematic, It's sweaty and confining, Think of a 10lb weight on your chest while trying to breathe.

If you allow it as a GM, I'd make any "sleep" gained be counted as 1/2 time (8 hours sleep = 4).
 

Thanks for the ideas. I think I will just up his chance to be surprised in any wilderness encounters the following day to 3 in 6. Basically just give him a heads up that he can sleep in his armour but not well and he won't be as alert.

I should also note that he is traveling alone (I am working on rounding up more players) so my player is thinking strategically. He is concerned about being ambushed at night.

I will remind him he can hire a merc to help watch his back. This might give him a tradeoff to consider.

I'm curious as to what he decides to do. 🙂

Since my pc's look to be sleeping in their armour now, here are my rough rules for tonight's session

subtract 1 hp from night healing rolls for each DR

If nightly healing rolls is less than 1 then the rest
isn't restful enough to recover spells.

For each night past the third make a Test of CN. If failed
then no spells are recovered and you are fatigued.

If Medium armour is worn that the test of CN is
done after the 2nd night

If Heavy armour is worn the test is after the 1st night

Fatigued meaning all rolls are at a -1 penalty. AC
is also reduced by 1.

I'll probably tweak as things go along