Temporary paintjob on dart swinger - matte grey?

i went to wal mart and bought a case of cheap flat black spray paint at a cost of 15.00, then 2 cans of red gloss krylon for another 6.00 to do the hood and rear stripe. i figured this way , i can work on the body while i drive it, then just sand it all off and properly prime and paint it when money allows. however when i did this, i just scuffed the factory brown paint, so there is protection underneath. i had a friend in high school that drove a primered grey valiant for 6 years before he got it painted. he never had any rust issues , and that was rattlecan, he just kept up on it.