downfire questions

i think I've settled on going with a downfire sub box in my suburban for my 2-15's. I'm going round ports so i can change tuning if needed. but can't decide where to aim them.
1- aimed down with subs
2- out the back towards rear doors
3- out the sides towards each side panel

also should i carpet under the box? it will have deadener and probably insulation for road noise and vibration. but would carpet be of any benefit?