Even though the BDR has stainless skins riveted in the foot boxes, mine were bleeding a tar like substance in the areas nearest the headers.
While I had the headers and sidepipes out for recoating this last time I installed Aerogel XTC 5mm insulation,
https://spinoff.nasa.gov/Spinoff2010/cg_2.html
BuyAerogel.com | Blankets
DEI reflective heat shielding on top as a top seal.
https://www.summitracing.com/parts/dei-010462
Edge sealed with Dapco2100 firewall RTV.
https://skygeek.com/d-aircraft-dapc0...-bms-5-63.html