That looks great! As for mats, just do a search for grilling mats and you should find them, or ask at any store that sells grilling supplies. Alternatively, before I got mats, I used to use wire cooling racks for baking. Just lay the cooling rack directly on top of the smoker rack, with the wires perpendicular to each other, thereby creating squares less than 1 inch per side. Then lay your fillets on top of both racks, and the fish should stay where you want it (but yes, more things to clean afterward).