i think its a bad idea to have all fans blow inwards. I have 3 fans (2 in front, one on the side) blowing in, and 2 fans (one big one in back, one on top since heat rises) blowing out. This helps the circulation to clear out heat and dust.
if you have all the fans blowing in then you basically also keep the heat in, so it fries as if it wasn't even in a case.