Need help building box

Ok I don't have a wakeboard boat I have just a normal runabout boat. I'm trying to install some subwoofers but need help with a box. I have two seat in the back and would like to put them there. One under each seat. Now I had 1 wet sounds ht 10as all in one sub and amp. This was very impressive and sounded real good for being just 1 10" sub. Well I decided to buy 2 wet sounds xs-12 subwoofers to replace it. They are being powered by a fosgate r1200-1d. I bought some rhino lined qbomb boxes that have 1.3 cuft. I know my sub requires 1.1. But didn't think .2 difference would make a difference. Well these 12's sound real boomy and don't hit. My 10" sounded way better an hit harder then both these 12s put together. Will downsizing the box make a difference to make them sound better? I have the space available for 16" wide, 15" high and about 22" deep max. Any way I can make a ported box in this space to the air space recommends? In the event that I have to go seal will a 1.1 box really make a difference from my 1.3? Thanks in advance