The width of this DOUBLE THICK Rail Gasket is specially designed for use with StarCat and Dauntless Evaporators, but could certainly be used for other evaporators as well. The gasket includes an adhesive backing, so it will stay in place while you set your pans on top of your arch.
Cut the Rail Gasket to length and lay each strip FLAT, adhesive side down on the Arch rails. Place your Pan(s) on top of the Rail Gasket. This will prevent air from being pulled under your Pan(s) which would cool them down.