They do take up some space and they are fairly heavy but don't let that bother you. A lot of good amps are big and heavy. This would be a great amp for a sub. There are a couple of series II DC300A's coming up on ebay and are just later models. Should have the same build quality but are dark grey or black and have a switch for bridging mono. They usually run a little higher in price than the silver or older models but I would not be afraid of any of them. By all means, let us know what you get and how you like it.
Bill