Oh yeah. Glue and screws ftw!! I've noticed with mdf, it does need to be the right kind of screws and exactly the right size predrilled holes for the screws for them to bite really well.
I doubt 2 3400s will be enough for 5k. I ran 4k for a while with a 270 amp alternator, 2 3400s, and lots of 0 gauge and my voltage would still drop down to around 12 volts