With all those potatoes, Don could use a root cellar.  There are lots of  designs to choose from.   Could you recommend one for him?

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Economical to construct, but not much space.  Would probably need more than one.

This one looks like the potato are escaping.

Also low cost - still not much space.

Might be confused with an outhouse.

More spacious, and cheap materials, but might not hold up to the elements for very long.

In a pinch, this could also work as a church. 

Good way to recycle an old tub.

Would require a good mason.

Also a good recycle project.  Comes ready made, but a mechanic might be needed.

Looks almost comical - but a definite conversation piece.

Functional, but looks a  little pieced together.

This one would fit in well with Belinda's flowers.

A little rough - and looks like a lot of shovel work would be needed.

In case you forget where it is.

A good use for those rocks off the garden.

Maybe a little too artistic.

Nothing like a good roof to keep the rain off.

OK, I think this is the one.  Maybe a little high end, but should last.

Maybe a little too rustic.

And what about the inside?  This should be enough room.

So you don't fall off the top.

He will need some good containers, too.