I built one a few months ago. It's quite easy and the instructions are good. You don't really need the grommets and dowels. Mine stays closed by friction alone. The trickiest part is getting the thermostat wired correctly, but there's lots of guidance available if you search online.
My one complaint about the SOFC is that it controls the ambient temp, not the temp of the wort. As a result, you have to monitor the thermostat setting and play with it to control the wort temp as fermentation progresses (i.e. as the fermenting wort generates different amounts of heat). I've recently modified mine (per the instructions on the Mother of Fermentation Chiller) to have a remote temp sensor (just a modified thermostat with longer wires on the thermistor). I haven't tried it yet (next batch), but I'm hoping that putting the temp sensor directly on the bucket helps.
I have noticed that good temperature control is probably the biggest contributor to the improvement in the quality of my beers. Clearly, more improvements are needed, but temp control made a huge difference.
A note on thermostats: I would not recommend Honeywell thermostats. They work great, but the thermistor is a little tiny carbon-ish thing on the circuit board. In my experience, it is un-modifiable without destroying the thermistor. The RiteTemp models (6020, if I remember right) uses a normal-sized thermistor that's on wires and easily modifiable.