1. Make the front end more aerodynamic.
You'll never be able to retire on the gas money you'll save. You're pushing a lot of air either way.
2. Virtually eliminate those pesky window leaks.
If they leak, put some flexible putty around them that can be removed before you sell it or have them fixed. Mine's 10 years old, and it doesn't leak. Never has.
3. Give us a central area to build an entertainment area.
You can build one or have one built, but when you go to sell your 'C', you've eliminated buyers with kids unless you make it removable.
