I have had about 5 games with MH now, 2 with Dunwich alone, the others with KH and BG. I am really enjoying what MH has done to my game, it has forced me to adapt my long used basic strategy and this has made the game more interesting.
Before, my strategy was probably the same one used here by most players: gather up enough clues for the first 1 or 2 seals, send them off while the others (I play with 4) deal with monsters and expansion boards or the odd rumour or other situation and gather their clues, then switch out when (if) the first 2 return.
This is no good for the mid-late game anymore. By then, you will have maybe 3 or 4 seals and you will be (often) scraping up the final 10 or 16 you need to win as fast as possible. And at this point, the statistics are very high that you will have a seal burst open and you will then run out of time vefore the Ancient One awakens. This has happened in every game but my last game, when I changed the strategy and won. Once it happened THREE times! MH ensures that you will at least SEE a burst card, and the odds seem high at this point that you will see more than one and thus lose a seal, ESPECIALLY if Kingsport is in play and whoah betide you if you add BG too.
So now my strategy is this: gather up ALL the clues you need in the start of the game. Do nothing but aim for this and fight off the tide a little if necessary (close gates for clues and to prevent there being too many open). In the early part of the game clues will be appearing more frequently so this is not as hard as it seems a lot of the time. When you have all or almost all clues go for all the seals at once, returning to the Science Building to top up clues if necessary/possible. This gives you a minimum amount of time for the seals to be lost. Ideally, place the first seals on the non-volatile unstable locations.
This way the game is actually more fun as you will spend the first third of it exploring the board, and have a mad race at the end where one delay or slip up can cost you the entire match. In this way, I won my last seal just before the first one would have broken.