Well, I think that im going to get the two 12'' and put them in a sealed. Im not even going to worry about the flex. No big deal, its inevitable (sp). But whoevers, eh?I have 70 sq feet of deadner in my trunk and still get rattle and flex. Bass will cause flex. period. No matter what. Just think about it really hard. Thin metal vs subs pushing tons of air. Subs win. Now if you realy want to get into it you could build a false lid with 3/4 mdf, that might stop it. 2 10's will probably sound better and get louder than 1 12. Surface area. And this is based upon you having the right box and the right power. Good luck.