I built the canopy on my 180.
I sealed it with Zinsser /Binz primer sealer and then water based poly.
The white helps reflect the light also.
The back of my canopy is open so humidity can exit.
I only have the glass cover(versa) on the back section with the middle /front completely open.
I also installed a computer fan to draw air through canopy if I need it.
When I use it I plug it into the lighting timer(one of them....).
You can see the back is open and the door is white.
I made my canopy only tall enough for lights (originally) and it opened on the top.
Then later(years) I built the door/riser section and just placed the original canopy on top!!!
2 pieces are lighter then 1!!!