Im looking at putting a solo baric in the back of my MSC with a set up like this. Do you think the box would big enough for the larger sub?

http://bonz.smugmug.com/photos/27636142-M.jpg

 

Box size depends on the subwoofer itself and the vehicle dimensions. If you are just looking for moderately acceptable level of sound quality you can follow Kicker's specs for recommended box volume. If you really want to control the response you would need to select a target Qtc based on your own preferences (do you want boom...accuracy...??), allow for cabin gain, and size the box accordingly - there is lots of info/folks on various forums that could help you with that, and there is free/low cost software available that will get you a reasonable approximation of the right answer.

Or you might not care about any of that (that's ok too!), in which case just put it in a box that will fit and remember that a smaller box will yield more output but less low freq extension (boomier bass), and vice versa.