Im just in the process of transferring system into new truck. I have used new ' FatMat' product called ' megamat' , which is butyl based and way cheaper than dynamat, on door panels and have round rubber deadening pads to go behind mids. I was wondering if I should make some kind of sealed enclosure around speaker and how to do it cheaply.

 

If you do a good job matting both sides inside your door (the inside of the interior panel, and the inside of the exterior door skin) you shouldn't need to build an mdf box. Assuming you aren't putting subs in the door, like this one guy I saw. He did no prep work, just cut holes and screwed in 10" subs with mid woofers next to em, and tweeters on his center console.