I picked up a military surplus Valad Heat Sealing Iron off eBay like one of these: http://www.ebay.com/itm/VALAD-SEALING-IRON-HS3T-150W-120V-HEATING-PARTS-TOOL-HOT-ELECTRIC-MILITARY-USED-/172624490089?hash=item283138ae69:g:Sb0AAOSwoydWqAl8
I didn’t have much luck with the clover either, this is much heavier and seems to hold the heat better. My friend Evan found a similar industrial sealing iron for $75 used somewhere that has a heavy solid iron end that works well too. They are both just about the same width as our seams.
His came with a teflon type cover which I realized was the same as my Excalibur food dehydrator sheets so i cut a small piece form one of those. This helps the hot iron from sticking to the fabric, especially when I first start and the center of iron is hottest in one spot. This works pretty well now.
I’m interested to see how the hot air welders end up too!