Well I estimate around 700 - 800 lbs or so just in the trunk. That is with the subs, amps, steel, and batteries.

The steel is actually very important for the hard hitting subs like I have (well as far as getting louder). What it does is it stregthens all the joints where wood/mdf meet in the box. It helps stop the wood from "Flexing" so that the energy created by the subs is forced more out of the sub port as pressure instead of energy loss in basic vibration inside the box. Granted vibration then comes out into the cab, but that is because the actual pressure is increased in the cab instead of in the box/out the trunk. Makes a good difference for sound pressure.

The resin then helps smooth and seal. It adds a "echo" effect in the box which allows the sound pressure to be more concentrated and sent out the port as well.
A lot of box designs are different.

But I can't wait either! it takes me a lot of time to make the angle, cut, shape, drill, then resin... then smooth and tape and screw, then silicone, then construction adhesive, then testing. It is quite a chore haha.

But I am excited - I will be the loudest Aveo on this green earth