Top board is the "ventilation board" which I like to leave out for vent when it's not nice out but more air movement below is needed. At the Seattle Fisheries Supply gear swap I got a 4" heavy brass deadlight which fits where the blue tape is. I have to shape the tops of the slots on either side and whack off some end bits of the vent board for a final fit.

For join at the boards I went with partial rabbetting and partial 25* slope for extra effect.

Damn cold today, wind, rain, snow in the low hills and 45* here. Brrrrrrrrrrrrr...........