Hiya!
EDIT: After a re-read, I'll just preface this with...: Warning! Old grognard curmudgeon opinionated stance below! Warning!
My group absolutely wants to play a mega-dungeon, Waterdeep: Dungeon of the Mad Mage. I am a bit worried on how to handle resting in such an environment.
You're the DM. How they handle resting in a mega-dungeon
IS NOT YOUR PROBLEM!
Sorry to be so...emphatic about that. But I see this rather bad DM'ing trait all to often nowadays; the DM think's it's their job to "keep the PC's going forward". It's not. They are not your PC's...they are your Players. The Players are the ones that should be the determining factor for their success, failure or death. Not yours. You should ultimately be completely unconcerned with their outcome...even if you may be secretly rooting for or against them. To quote Basic D&D:
"There is one rule which applies to everything you will do as a Dungeon Master. It is the most important of all the rules! It is simply this:
BE FAIR".
This means what I said; it's not up to you to 'help' or 'hinder' the PC's based on what you "want".
I usually try to have some story reason that encourages the players to push on, not taking a long rest after every major encounter. I don't see that working in a mega-dungeon. "You can't rest here, it's not safe" isn't going to work either, as obviously at some point they will have to rest there.
This is something that immediately sends up a red flag when I hear a DM utter it. It tells me that the DM is "deciding" the outcome of the situation and that I, as a Player, have no say when it really should be all up to me weather or not I succeed or not.
Again, you are the DM; it's NOT your job to protect the PC's! You, as DM, know the chance and frequency of Wandering Monster's (or you should!), and you know what is in the other rooms around. If the PC's try and rest, let them...and start rolling for encounters. Even if you know it is 100% safe...roll those dice! It keeps the Players guessing and it keeps up the uncertainty and 'tenseness' of the situation.
So I am wondering whether I need to add some new house rules to the mega-dungeon to prevent the group from resting too often.
What do you guys think of a rule that players get half xp for the first fight after a long rest?
No, you don't. As I said...it is NOT UP TO YOU to decide if/when the Players say "Ok. We're gonna rest up in this room for a few hours...taking a Short Rest". That's on them. All you do is look at how active the area is, what monsters are near by, and then figure out the chances of the PC's being discovered/interrupted. Then you roll dice and STICK to the results!
My suggestion? Go find a 1e AD&D DMG or buy the PDF off of DriveThru. Read it. Alternatively, if you can find a copy of Hackmaster GMG (4th edition; NOT the 'new version'), that'll work too.
Oh, a really great thing that I think every DM should do, is try and find as many 'old' Dragon Magazines (pre-3e) and read them. There is sooo much info in those from all types of RPG'ers (not all good advice, btw, but hey...interesting none the less).
^_^
Paul L. Ming