"Real" automotive paint (base coat / clear coat) is much different than rustoleum chemically. Both types of paint have advantages and disadvantages.

The primary advantage of base / clear paint is superb resistant to UV light. UV light from the sun causes the surface of paint to "chalk". Base / Clear paint is very resistant to this natural process. It will look great for many years even if the vehicle is always outside. A second advantage of base / clear is excellent corrosion resistance.

The primary disadvantages of base / clear paint include: It's dangerous to apply requiring personal protective equipment. It should not be sprayed in some places. (townhomes for example) It requires a large (expensive) compressor and other equipment for spraying. When sprayed the overspray goes everywhere!

Rustoleum or similar paints, when applied as recommended in this tread and given several months to dry, are quite scratch resistant. These paints are comparatively easy to apply with very few health risks.

The primary disadvantage of Rustoleum is it will chalk and start to look bad after a period of time. (1-2 years) 69Charger, the originator of these posts, has recommended frequent waxing to slow the chalking process. When the paint chalks, rubbing compound / polish will bring back the shine.

I know a fellow who sprayed synthetic enamel on an antique truck approximately 20-25 years ago. (Synthetic enamel is very similar to Rustoleum) His truck still looks fine. Of course his truck spends 360+ days a year in a climate controlled garage under a cover. He washes and waxes it regularly. I'd be surprised if this truck has traveled 5,000 miles since he painted it. He probably has the ideal conditions for paint to last.

In summary, every type of paint has a "lifespan." How long a paint lasts is determined by the environment the paint is in and the level of care given to the paint. Which type of paint a person should use is very much dependent on their situation and the intended use of the vehicle. There is no correct answer for everyone. I'm using rustoleum on some parts of the car I'm restoring. (such as interior metal parts) My current plan for the outer sheet metal is base / clear. I like the look of base /clear better and I like the lower maintence of it.

Edit: I'm thankful for the posts on this method. I'd never considered using rustoleum anywhere on a vehicle till reading these posts.