Well since you asked
I've seen these threads before.
I don't care what you've read on other sites. I wish I could give you a vote of confidence as others have in this thread but I can't.
I'm gonna be honest.
I've been painting cars for 35 years. Contrary to popular belief Rustoleum is not an automotive finish grade product. I use it alot myself. Its great for small engine parts, deck chairs, bbq grills, kids toys, industrial tools, ect, ect, ect.
If you paint your Mustang with it:
#1 It's gonna look like poop.
#2 It's gonna take alot of product and multiple coats to achieve gloss and a "Decent" looking overall finish at best.
#3 After applying massive amounts in hopes to achieve a decent appearance, Durability will be compromised!
-Rustoleum gets softer and softer when multiple coats are applied and takes longer and longer to dry.
-It may never totally dry.
After a month or even two you will be able to use your finger nail and scratch the finish with little effort. If you should spill gas on it while fueling your car it will damage the sheen or cause it to craze and/wrinkle. On a hot sunny day you will be able to mash a thumb print in the hot finish.
Bottom line its not up to the task and I hate to see anyone waste time, effort and money going down the wrong path.
Trust me do yourself a favor, save your money and buy real automotive finishing materials or take it to a body shop and do it right.
good luck