Melt butter in a Dutch oven; add onion, and saute until tender. Add corn, and cook, stirring occasionally, 2 to 3 minutes.
Stir in pumpkin and next 5 ingredients; bring to a boil. Reduce heat, and simmer 5 minutes. Stir in half-and-half, and cook until thoroughly heated (do not boil). Pack in a thermos.