Yeah, assuming you mean a metal post and metal frame I'd use the white grease. Just enough to make a thin coat. The purpose isn't so much in aiding the insertion of the seat post but to prevent corrosion or galling that makes removal difficult or impossible, so you want something thick that will stick around for a while. The tri-flow and ultra-lite oil are way too thin and I've never heard of TriGEL but I've successfully used white grease many times for this purpose.