Your PUD is currently offering a $160 rebate for air-sealing pre-1992 manufactured homes through participating installers.
Air Sealing and Insulation Brochure
Please Note:
Air leakage, or infiltration, occurs when outside air enters a house uncontrollably through cracks and openings. Air-sealing cracks and openings is one of the most significant energy efficiency improvements you can make to your home. Air sealing will not just reduce energy costs; it will also improve your home's comfort, durability and air quality.
Sealing and insulating the "envelope" or "shell" of your home (its outer walls, ceiling, windows, doors, and floors) is often the most cost effective way to improve energy efficiency and comfort. ENERGY STAR estimates that a knowledgeable homeowner or skilled contractor can save up to 20% on heating and cooling costs (or up to 10% on their total annual energy bill) by properly sealing and insulating.
Source Material: US Dept. of Energy