A very easy thing to do is make a mock-up of the box. Measre the trunk and openings to see what size box you think you can fit. Figure out what size the box needs to be based on those specs. Get some cardboard and fab up a box the same size as the one you intend to build. Just use some tape to hold it together. It dosent have to be pretty just needs to be the correct size. Then try and fit the thing in your trunk thru the lid or thru the rear seat opening. If it fits your golden, if it dosent figure out what adjustments need to be made and try again.