the plywood flexes much more than the MDF will, what ever the size i always go with 3/4" MDF, its a difference if $10 per sheet over the 1/2" MDF. a sealed box requires more power to produce sound than a ported enclosure. a sealed is better for listening to rock and metal and a ported is better for rap and deep bass.
for a sub enclosure you can make it a down firing box to help hide it from people walking by that may want to take it. if not you can always bolt it down to keep it safe.
i took out my rear seats to fit my large ported enclosure in the back and purchased a bestop extendatrunk to hide it when needed
Now i lay me down to sleep, beside my bed a glock i keep, if i should awake with you inside, the coroner's van will be your next ride.