+1 Amazing subThe Image Dynamics 12IDQ version 3 would be my choice. The IDQv3 subs are awesome when it comes to clean accurate SQ and hey get loud and hit super had too.
For some reason everytime i have heard Troe subs i have been let down, they get loud but seem to have a 1 tone bass.Between JL and ID certainly go with the ID, also look into Treo SSi's.
I would think the same will be true about MDF, it just tiny fiber particles with a binder? I think you will have to treat your MDF box as well. If it were not for cost, you might consider marine grade plywood.Couple reasons for the switch to MDF:1. I live in an area that has a tendency to have extreme climate changes from time to time, I have heard that fiberglass enclosures can be cranky with things like that? They can also flex more and generally be more sensitive to damage? (Tell me if I am wrong here)