Prepare campfire or grill for medium heat. Spread butter in the center of each of four pieces of a double thickness of foil (about 12 in. square). Place one salmon fillet in the center of each; sprinkle with salt and pepper. Top with onion, garlic, dill, basil and lemon. Fold foil around fillets; seal., Place packets on a grill grate over a campfire or grill. Cook until fish just begins to flake easily with a fork, 8-10 minutes. Open carefully to allow steam to escape.