Yup your going to need a lot thicker then that, just my top desk I'm thinking of getting is 3.5mm and thats over 1/8 I believe? so for the chassis you would want something decent..
My Aluminium chassis is 3mm thick.
Oh yeah, also you will loose a lot of cooling!
Alloy chassis acts as a big heatsink to cool the engine (sucks heat from crank case)... You may have temp problems with carbon chassis?