I think you're talking about the cover over the fan over the "kitchen"? I replaced my whole thing (in my 1707T) with a Fantastic Vent Fan. It's a "standard" size and was pretty simple to replace. I think replacing just the cover would be dead simple.
The cover MAY have a plastic insert that can be cut if it's too deep. My new fan had this and trimming was expected.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew