I was just wondering what are some of the best ways to keep impedence rise down. I have read that it doesn't matter much in daily but I don't see why that is true, unless it is only a db or so difference. Are there box designs that make a difference or cooling methods?

Not cooling methods.

Your best bet would be to download a box building program and look at impedance graphs in various enclosures for a given sub and see for yourself.

But modeling up my sub, ported box size plays little part in maximum impedance rise. However, increasing tuning frequency increases the bump in impedance near the tuning frequency, but the upper impedance hump, 5-10 hz above tuning, decreases with increased tuning frequency. In a sealed box, impedance rise is higher in larger boxes and also moves lower in frequency as box size increases.