The reduction in ground clearance on the Trade Wind did not cause any problems back in Minnesota. I did take a straight edge from the rear tire contact patch to the rear bumper and the "departure angle" cleared my tank pan. A center bath allows even more "departure angle". Here is a photo of the pan around the tanks. It is 4" below the frame rails. My 86 Limited is about the same size.
Some Airstream boondockers take their trailers up old logging roads or mining trails. Very rough roads with big rocks and washouts might damage the tank pan. I don't use my Airstream in this manner.
Here is a thread of a AirForums participant who built a center bath in his 68 Trade Wind. It may offer some ideas for you.
Yep, the easiest way to repair a broken bathtub is to start over with all new. I built a new bath in the rear of my Trade Wind. No bathtub repairs required.