you are WAAAAAAAAAY better off with getting a R4 instead of a 300R. better cabling, better IO, better fans, and would be more sturdy than adding foam to the case. and the foam that you buy isnt as good as the fractal stuff in terms of quality
so just get a R4
and id recommnd this power supply. dont cheap on the power supply. its the component that keeps the system alive or just completely kills it.
this unit is based off of the seasonic m/s12ii platform. a bit newer and more efficient than the one on the antec basiqhttp://us.ncix.com/products/?sku=59615