Cleaning the bottom of the box....

I taped the upper box with a sheet of plastic before taking the pressure washer to the bottom....It's not near as rusty as I thought it would be.....Just alittle in the left rear corner and it's not bad at all....Now the question is...Do I spray paint is or brush it on.....Brushing would be cheaper and I could match the paint better....Not sure what it would cost to get the coke red matched and put in a spray can.