need help with dimension with building a box for two 15s

[Kody3232]

So I'm looking for some dimensions for building a box for two alpine type r's dual 2 ohm there 750 rms each but im trying to build it for a 1997 ford explorer xlt 4 door i dont want to build a huge box because i have to be able to fit it in a car to take it to the explorer but i want it to have a bigger port then it calls for some people where telling me i should make it 8 cubes but that is way to big this is my offroad toy im putting it in only drive it in the winter time and on trails so im gonna use L brackets to hold the box down i have a rockford t1500 that im hooking them up to i just need help with what i should kind of box I should build i heard birch is good wood but im in a budget with this build so need some help