going to herc the jeep, got a ?

hey guys, i recently removed the carpets and, being from ny, had to repair at least a dozen rust holes. i have painted the floor flat black rustoleum already, but i want to herc it too, to protect from rust and keep it looking good for a while.

but i have a few questions, how much of the stuff did you u guys use,
also, im kinda hard pressed for cash right now, have any of you had experience with the duplicolor bed liner stuff, my friend used the spray stuff and it seemed like it was the same stuff. just wonderin if anyone had any experience with it,

thanks
travis