Being a manufactured home, I guess you can't put more insulation in the
"attic". Also I think if you install a new furnace, it needs to be approved
for a manufactured home?

Anyway in general there are things you can do to reduce your energy use.
These things cost money, but will save in the long run.

- Buy new "Energy Star" appliances. They use less electricity or less hot
water.

- New gas furnaces are very efficient using less gas and electricity to run.

- Add more insulation.

- Use compact flourescent bulbs *everywhere*.

- Heat just your bedroom at night instead of whole house, Use electric space
heater. Saves money if you are using just one bedroom.

More tips...
http://www.energystar.gov