Prime & Paint underside questions

I used rustoleum rust reformer on the bare metal then go over that with rustoleum stop rust paint.The good thing is you do not have to sand the rust reformer before you spray on the stop rust paint.It says rust reformer and stop rust paint right on the cans.You can also go over that with rustoleum undercoating.It all lays down smooth and looks good and its cheap.I wish i had listenened to a guy i know that has built cars for years and told me about it before i spent all that money on eastwood stuff