Bull.

What direction is the seam running to the light source? Most mills recommend perpendicular to the light source. How heavy of seam tape you use? Peaking is something that can't be stopped short of hand sewing the seam, it is a nature of physics when you add something below the seam and put stretch on it. The tension wants to go in a straight line so it follows the seam tape forcing the center up causing the peaking. Now using the thermo as a sealer will help because it welds the two edges together and don't let it rise. Another scenario is maybe it isn't peaking as much as it is seam profiling from to heavy of a tape. If you can see the tape line then that is what it could be. either way I would thermo seal the seam and use like Orcon's SU-90 type seam tape or equivilant. It is a low melt urethane tape so clean you iron before using it and run your iron on like 2. Or even better if you have a Kool glide iron use that. Rereading your post I'd say you have seam profiling-to heavy of a tape, but there is still something under there. Even a newspaper would show up in time. Daris