sub box for 2 kicker cvr 10’s

Never use a box with airspace less than the minimum that the manufacturer suggests.  Those minimum recommendations are going to produce boomy sound with very little low end extension...but reasonable bass output in some user's opinions.  Everybody knows the space limitations when dealing with car audio, and the manufacturer is just as aware of this as anyone.  They make such recommendations so that their products can be made to fit into just about any vehicle application.  That doesn't mean that the .8 cu ft size will sound anything like the 3 cu ft size.

I suggest contacting someone who is good at building custom enclosures to have a look at this.  He may want to work a solution up for you using some software, and he may also want to build two enclosures instead of one so that they can be fitted through the trunk opening easier and then arranged and fitted within the cargo area.