I'm putting in a new front trunk seal and want to know which seal face goes against the body (or alternately faces up). The seal has two flanges one is thin (relatively) and the other is much thicker. Any guidance is appreciated. Thanks.

The thicker part goes into the channel and should fill the channel completely.
The thinner part should be flexible and form a seal against the hood.

Good seals don't need to be stretched to fit into the channel ...

Thanks Andy.
That's how it's going in.