Descent Campaign Shortening
While this may seem disappointing, my advice is: don't.

Descent is a great game in its single-dungeon mode, and while it might look appealing to bring your characters from a dungeon to another, it actually "just doesn't work".

One of the fun things about this game is the weapon progression: as you go on, you might find cooler weapons to use. This works well in a single dungeon, but is crap in the campaign: after just a few encounters it is likely that every player will have the best-in-slot weapon for that campaign level, and anything else they can find will just be sold away. This takes away a lot of fun from the game.

Moreover due to setting and stuff you end up wasting so much time playing just a couple of (short) encounters in the campaign, that you could have played a whole (much longer) dungeon in the standard game.

If you really want to keep a few things from one dungeon to another, you could keep the same characters, follow the standard rules about xp and progression, and change a character with another one if he dies.