I don't know what product your using as I have only used pro stuff from the body shop. And not on a sub but on my blazer. The look is very similar and it covers quickly if it's not being absorbed into the wood. If you don't prime well the result may vary on the box and you don't want that...
I would suggest you definitly prime first for an even lay down. Are you speaking of what is often refered to as Chip Gard or Stone Gard that is used at the body shop? Comes in spay cans also. If you are, it's very easy to use, but be sure to sand and prime first. Super easy to use and...