Honestly that one is a little tough to offer suggestions for. If you don't have the subs already then when shopping look for subs that require the least air space. Definately go sealed, as all other box types require lots more room. When laying them out in the trunk I wouldn't recommend that you have them firing directly at one another...they will not sound as good. Not sure what else to say...good luck...post pics

 

rice eater. For all the work and the money. wouldn't it be easier for him to just get 2 really nice ones?

 

IMO, yeah I wouldn't use more than 2 subs in the trunk. You'll be able to buy 2 better quality subs instead or 4 lesser quality ones (that is unless money is no matter in the case). The box will be easier to build...and will probably look better because you aren't trying to cram so much into a small area.

But the OP was asking for opinions on getting 4 subs in the trunk, not how many to get. Thats why my original repsonse was what it was.