Since it is a diesel, be SURE to add a load of diesel fuel conditioner AND a load of fuel biocide to the tank, mix it with the fuel and drive the car 10 miles to be certain the protectorants have fully circulated through the engine. Then top off the tank and hope for the best over the winter. A load of algae in the fuel is to be avoided at all costs. In the spring, I'd add another shot of biocide first thing.
I'd also do an internet search on the general subject of storing cars and possibly speak to an auto museum curator. Every input helps.
Don't forget to drain the windshield washer tank and lines.
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet
'86 560SL 124K Miles
'94 320E Wagon, 74K Miles