Is there a true rba (in the style of a Genesis, AGA-T, RSST), that is a bottom coil instead of top coil tank? I would love to know, since I am impressed with the Kanger ProTank, and am looking for something that has the same features, but is a true RBA. I know how to rebuild coils on the Kanger ProTank pretty well, but want an upgrade of sorts lol.