I agree with Luke ... 1' x 1' would be great.
Jason: I also highly recommend you order the Enkamat 7210 (flatbottom) variety. PF4 is Enkamat 7010. The 7210 flatbottom Enkamat does much better on startup and produces finer bubbles. Others disagree but I have modded over half a dozen pumps now and with each I get better foam, lower watts, easier startup and higher air from the 7210.