Does anyone know if seam sealer is recomended behind this area where the tail panel meets quarter but isn't attached except above and below? Specifically at/behind the joint.

I used sem seam sealer on the last one we did, it's a 2-part sealer..

can anyone post a listing of which panel/seams should be resealed in a complete build (where all sheet metal is replaced). Thanks

Basically any seam that is exposed to water or that could hold water....
rear body panel interior/ exterior
trunk floor to drop off seams
trunk floor to inner wheel houses
inner wheel house to outer wheel house
rear window filler panel to 1/4 seams
1/4 panel to rocker inc jambs
rocker to 'A' pillar
drip rail to roof seam
firewall to cowl seam
cowl side panels
upper door hinge to 'A' pillar
cowl seam to upper dash panel
door skin to door shell
seams under the roof rail weather strip retainers
deck lid skin to inner structure
That should get you started, probably a few I missed