I agree with @simplesez that the Sprinter cats are well protected. But on a more vulnerable vehicle, perhaps a stainless perforated sheet under the cats to make it hard to quickly get to them yet let the heat out. Will cost money, add some weight, take some brackets to support and defect some heat back to the vehicle body and other parts, so have to access if worth the risk of cats being stolen. I'll bet that vehicles with cats stolen is probably a million to one, even thought we hear about the few that it's happened to it seems like a much larger issue that it statistically is.
Owned a 2007 Sprinter poptop and now a self-converted 2016 170" 4x4 with aluminum/HDPE cabinets, hot water, air compressors, electrically raising bed, bike garage, rotating bench, custom rack, suspension, skid plates, lights & more. Build out videos at www.vantripping.com and https://www.youtube.com/c/KCMares.