i would get a wiring harness adapter to connect to the factory harness in the dash....then solder/heatshrink wires from there down the driver's side of the truck into the seat rail (it has holes through it under the carpet) then under the seat..cut a small slit in teh carpet for the wires...since u have the seat out its a non issue to peal the carpet back to see where the any stock underseat harness is located..this will help to tell ya where u can drill holes...usually there is one or two harness' depending on if u have power seats or not from what i recall....look under the truck to be sure there are no brake lines, etc., then loctite self tapping screws and screw down the kenwood units...if they dont come with screw holes then go to home depot or any car audio store and purchase metal straps and bend a couple to shape and screw them down around the unit, using weatherstripping to isolate the units from the metal straps so u dont scratch em....this is not really a tedious install because u can do most of the soldering in the comfort of ANYWHERE other than under the dash

and the kenwood units i assu,e use BUS cables which u can also run with the speaker wires..u might even wanna zip tie the wires together but be sure to leave enough slack for the speaker wires to go to the passenger seat in case u decide to add an amp later..much less work to just move the wires over than to pull down the dash....makes for a neater and safer install...the really cool thing about doing it this way is that if in the future u want to add amplifiers u already have speaker wires under the seat that go to the front doors.....
IMO u don't need MDF...i don't use it and have never had an issue with wiring or mounting integrity....
Kevin