I have done a lot to insulate my vehicle for sound, and for heat retention.
I've added additional undercoating, especially around the underside of the
front of the van. I've insulated the doors, floor, walls and over the engine
with a type of bubble wrap between layers of tin foil. (Good for heat
retention and surprisingly good for sound protection.)

However, I get an unacceptable level of noise from my passenger side door.
It's the door seal, I know, but the price of a new seal is too much. Does
anyone know of a method for correcting this problem short of installing new
door seals?