It will house 2 RF P212d4's. Not the new black models the older ones with the removable magnet cover. I would be able to design one but I do not have the manual and rockford's website does not either. It is going in a Scion TC so I am going to build it to specs which is 1.75 cubes per sub. Tuning anywhere from 35-40hz. I will be powering them with a Diamond D3 400.1. Height cannot be more than 12", W cannot be more than 40", and D cannot be more than 16". Someone please design me a good ported box for these woofers to these specs. Thanks.

Don't even have 3.5ft^3 gross with those dimensions.

Yeah I just notice that does not give me enough space. I can do 12" H 39" W and 20". Any suggestions?

That gives you 4.2ft^3 before port, driver & bracing displacements... still too little.

To be able to fit that size & a good sized port, you need ~5.5-6ft^3 gross.

6 inch round port should fit in there fine

is there no way you could make the box taller?

I might be able to do 14" in height and the rest of the measurements the same