Any good modules/kits to build 300w MOSFET stage amp?

I'm looking for some way of building a couple of portable (think "I can
lift it and carry it upstairs in one hand") active speakers for use
with keyboard and/or bass guitar for occasional gigs. I anticipate
using a seperate preamp. There are a few 100w modules about (built a
Maplin one a while back) but anything more like 300w? I'm thinking of
reproducing a Roland Cube or Polytone type cabinet with 12" or 15"
speaker. All ideas welcome. Andy