Printer enclosure heater cowling

I've had real trouble with thin walls splitting apart, particularly on larger prints, (a. because they're larger, b. because the take longer to print -- i.e., overnight, and my printer is in an unheated shed). See last picture.

Figuring the ambient temperature drop at night was the main cause, I decided to get an enclosure heater. And an inexpensive temperature controller. After installing and testing the heater, I found that using as just a radiant heat source was heating the enclosure surfaces near the element too much, so added a low-speed AC cooling fan (on the same relay, so it comes on with the heater. That solved the too-hot-in-one-spot issue, but tended to blow warm air onto one side of the print.

So, I made a cowling that funnels the warm air to the bottom of the enclosure, and to the front and back; to more evenly distribute the air.

The "stripes" you see on my 'top half' part are pieces from the first, horribly split, part glued onto the second print (that faire