Make sure the clams and mussels are all alive. The shells should be tightly closed. If they're open, they should close when you tap them. If any remain open, discard.
Build a fire in your covered grill and soak a couple handfuls of wood chips in water. Put the potatoes and onions in cold, salted water, bring to a boil, and cook for 15 minutes, till potatoes have softened. Drain. Pull the husks back from the corn but leave them attached. Pull off all the silks, then pull the husks back into place and tie around the corn with a strip of husk.
Drop the lobsters in boiling water for about 3 minutes till they're bright red. Remove from water.
When the coals have burned down to red-hot, spread the wet wood chips across them. Lay the lobsters close together on the grill rack, spread the shellfish around them, and spread the vegetables over the top, ending with the asparagus lying in a single layer at the top. Put the lid on the grill and open the vents. Cook for about a half hour, until the mussels and clams have opened. Serve with bowls of melted butter.
Recipe courtesy of David and Sharon Bowers's Bake It Like a Man. Published by William Morrow, 1999.