Hey,
I have the same oven for 2 yrs and i have not change the catalytic panels yet. But of course i didn't cook things that are too oily in there. Just cakes, cookies, and some meat grilling occasionally.
Have you check with brandt office how much they selling the panels? It is definitely cheaper than the shops that sell them.
I didn't use my rotisserie function as it goes really messy. I just bake the chicken and turn it to brown more evenly.