Adam,
The black tank on our 71
Sovereign had to be dropped from the bottom, but then again, it is a
Sovereign, not a Globetrotter, so your setup might be different. I do know that, once the belly pan on ours was dropped, there was a galvanized pan (or what was left of it) with insulation holding the black tank in place. That galvanized pan was held in place by two L-shaped brackets, which ran perpendicular to the frame. What had happened with ours was that water had gotten down into that galvanized pan, which eventually rusted out, leaving the black tank unsupported. The black tank then cracked in two spots. Hope that helps.
Frederic