Pan Gasket at Rear of 2X6 Sap Pan?

[Sweetrun]

I have a Leader 2X6. Do I need gasket material along the rear of the sap pan? The pan is pushed up tight against the rear of the evap, and I have gasket material under the pan on the rails. The rear of the pan is not supported like the sides by the rails. It is a small 1/8 gap between the pan and the evap frame that makes up the collar for the stack. Is it ok to leave open without gasket material?

Thanks.

[WESTVIRGINIAMAPLER]

As long as your arch is not pressured as an airtight arch, the gap will be fine. Kinda cool to watch the fire shooting back thru there if you are not running a blower and with natural draft. Even an inch or so gap is fine.