I have the carpet and seats out of the maverick. I have some suface rust and a few pin holes. I am planning on painting the floors with rust bullet and wonder how much I'll need
I used just under a gallon on mine. Probably be about the same for you if you plan on fiberglassing it.
Gallon sounds about right for 2 good coats. I recommend using the quart cans - costs a bit more to buy but they are easier to mix up well and less trouble than sealing up an open gallon can while waiting between coats. Even if you buy too much - you will find other places on the car to use it all up.
I used 2 pints on the floor pan, inner quarters and trunk area http://1bad6t.com/Maverick/mav_2952.jpg
Cheap at twice the price, IMHO - compared to replacing sheetmetal ......... The only comparable product for quality I have used is Eastwoods Rust Encapsulator and that is priced about the same. Encapsulator comes in a few colors too which is nice.