I'm no historian, but consider your facts. If this rich guy goes out and purchases or has made a special chest designed to be extra-secure, he's announcing to all of France that he's about to hide his valuables. Times of social discord or upheaval are also times when thieves and thugs thrive because the law and order folks are otherwise engaged.
So I think he'd be likely to use the strongest and sturdiest locking box he already owns, arousing no one's suspicion. He'd probably bury it himself rather than having it ordered, too. The fewer people who know, the better.
My best guess would be that the box made in France would probably be of stout pieces of hardwood, probably oak or yew, well joined, with a brass lock and brass reinforcement of its corners and possibly its vertical edges. It would be reasonably attractive and secure until somebody with an axe got hold of it.
However, by the time of the French Revolution, German money chests were no longer new. Does your wealthy guy have reason to own one, or might his father or grandfather have used one when they started the family fortune? They're stout little chests, some lovely and some utilitarian, of wrought iron or cast iron. Here's one:
http://www.christies.com/LotFinder/lot_details.aspx?intObjectID=4934763
Okay, on to what shape the chests would be in. The wooden one will have rotted to nothing in normal soil, and its brass pieces would still be intact, although discolored. (We've buried pets in wooden boxes which were nonexistent except for nails and clasps in ten years. No skeletons remained, either.) It might survive if it was hidden away rather than buried. Is there a family mausoleum?
The German iron chest will be pretty rusted but might still be a chest depending on how often it got wet and how much of the air necessary for rust got to it.
What would he put in it? For the reasons he'd be unwise to buy a box, he'd be unwise to invest in easily-transported items of value. If he's smart, he'll consider how the item would fare if buried for, what, ten years? That's a long war. I'm thinking the entire family's jewelry, gold items like tableware and candlesticks, gold and silver coins, small
objets d'art of metal or ivory. If he's not so smart, he'd bury papers (i.e., deeds to land and houses), small paintings removed from their frames, paper money, etc. (Did they have paper money then?)
Smart or not, he might include anything really precious as a family heirloom, regardless of its value, as a means to safeguard it.
Maryn, thinking what she'd put in her little iron chest