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The problem with anything that adds heat to a system (oven or crock pot) is that it could keep cooking your tenderloin well past your desired temp. If I had to do this, I would probably FTC with some hot towels (soak 1 with the hottest possible water from your faucet and put it on the bottom).
Personally, when I cook a tenderloin for a crowd, I usually make the cooking of it part of the happy hour as it adds entertainment/conversation value to the evening - I do it Lomo al trapo.
This may not work for you on this occasion because it sounds like you want to be done cookiing before the guests arrive, but give it a shot sometime.
XL BGE, Klose BYC, ProQ Excel, Weber Kettle, Firepit, Grand Turbo gasser, and a portable Outdoor Gourmet gasser for tailgating
San Antonio, TX