New Build (looking for advice/input)

[Rflivinloud]

First off I am new to this site as a member but have found alot of really good info browsing. I will start with some details the vehicle for the system is a 2015 Chevy Sonic Hatch so not alot of space unless I fold the seats, but not an option at the moment. The sub is a Soundqubed HDS208 and the amplifier is a Soundqubed Q1-750. I'm looking for advice on type of box to use to get the most SPL out of it without sounding terrible. I have looked at the specs on the site, but would like info on other designs that others have used or if going with a normal build would be best. Also is there anyone that is running one of these that has ever had it metered? Just curious on what the potential is. I would also be up for suggestions on a different brand in the same price range same size sub. I know 8's are not the normal choice for SPL, but my goal is to be competitive in a lower class with something small (non sanctioned small events). Thank you in advance for your time.