I've got a drive that's at least 10 years old & has never flown. It's pristine inside, but spent most of its shelf life in relatively dry Arkansas (compared to MS, anyway...). Do you have any way to pump fresh oil through the bearings to get the used motor oil out? Might not be critical since there probably aren't a lot of hours on it (sorry, Chris...), but that's the most likely source of corrosion if you can keep it dry inside the case.
Certified a/c engine guys are paranoid about corrosion (a/c engines corrode readily, and repair costs are heart stopping). An engine that will be stored for a long time (more than a few weeks, in some cases) gets 'desiccant' spark plugs, bags of desiccant stuffed into every orifice, and then everything sealed up. SOP is to check the desiccant plugs every few weeks, if possible, to see if they've changed color, indicating that they've absorbed moisture. If found, they are baked to drive off the moisture and re-installed.
If you're not familiar with 'desiccant', it's the bags of particles you find in boxes containing pricey products that spent weeks in salt air making their way to store shelves.
Should work for both the engine and the drive. The drive could be cleaned, re-lubed with fresh oil, and put in a big seal-able container (like Tupperware) with desiccant bags. (Dollar store storage bins won't do it.) Harder to box the engine like that, but a big heavy duty trash bag might help keep out most of the moisture, if you can seal the opening with good tape. Or roll it in multiple layers of shrink wrap.... :-)
Charlie