Could you explain what a git trailer is if not appended to the message body? My understanding is that trailers are just key-value pairs in a particular format at the end of the message; there's not an alternative storage mechanism.
Even so, trailers or message body might be moot - rerolling the committed at timestamp should be sufficient!
Trailers are part of the commit message, but are separated from the body by a blank linke:
This is all one commit message, but it is understood by convention has having several parts: subject line, body and trailers.