Seam sealer, finished with a brush, factory-style, followed by Schutz!
It took a lot of practice with the Schutz gun to replicate the factory texture, but we've got it right. Hard to see in the photos, but it's the rough, sandpaper-like texture, not the smooth, dime-sized waves of the LWB.
It sure was hard to seal and Schutz over the pristine underbelly of the car, but that is what must be done to be original!