Rewton, Thanks for bringing that up. I did give the drain hole on the side some thought and was a little concerned that the hole might provide some beneficial exchange of air for the roots. This SIP is built using the same concepts as any other, only a little smaller (It is by no means a "mini" SIP). As such, and following the same basic principals as any others, I did not find any mention of drain holes providing needed air/gases for the roots in any of the tutorials that I looked at. That doesn't mean the drain holes are not necessary. They just don't work for me right now. I am watering with Gnatrol water and I don't want it to spill out in the house. When the plants are moved outside in the spring, I will definitely drill the holes. If you happen to find any articles relating, please let me know.
As for the gnats getting in the top; I'm hoping that any gnats left over will shy away from the dry soil on top. If not, I am still using yellow sticky traps, carnivorous plants, Gnatrol and a bevy of really bad curses. The option to easily close the hole in the top with a small piece of plastic is always available too.