I think they sound a little boomy and loose in the bottom end with the ports sealed up. Box is 3.6 cu ft or so.I would like some very powerful and clean sub action at 30hz or so.
Just sealing the ports will not create an adequate sealed enclosure. Generally speaking, the ported enclosure size requirements for a specific sub are double the size of its sealed counterpart. An overly large sealed box will give the performance you described exactly: sloppy transient response and an exaggerated bottom end.