In my house the treasures collected on past shelling trips fill every
available inch of shelf space and furniture tops.  But it's often difficult to
find ways of propping them up, especially the ones with round bottoms.  I've
tried all manner of stands and bases, with middling success.
 
But I finally stumbled on a way that works pretty well -- circular strips of
plastic cut from plastic bottles.  Cut cross sections all the way through the
bottle, about an inch apart, yielding circular belts of plastic.  Use a fine-
toothed hand saw -- a cross-cut saw, back saw, or hack saw.  The hardest part
is holding the round bottle still while cutting.  I used my husband's
workbench wood vise;  but even that didn't get a firm grip on the bottle,
which kept slipping.  I also tried my Dremel tool with a tiny circular-saw
blade -- holding the bottle in one hand and the Dremel in the other.  (Wear
goggles!)  We were afraid to try using my husband's table saw.  He briefly
tried a reciprocating "sawzall" with no success at all.  We don't have a band
saw, but maybe that would work if you could safely hold the bottle in both
hands while cutting.
 
As to the bottles, clear plastic is nicest, to obscure the shell the least.
Large cola bottles and milk bottles are too flimsy.  If the shell is shaped
such that the line of contact with the plastic is more oval than circular,
you can shape the plastic "belts" to form-fit the shell in a couple of ways.
First, use tin snips or heavy scissors to cut crescent-shaped wedges out of
opposite sides of the belt, making the belt narrower on opposite sides.
Second, you can squeeze the plastic belt into an oval and hold it there with a
piece of duct tape or, better, clear plastic wrapping tape.  Apply it such
that when the shell is resting on the plastic belt on the shelf or flat
surface, the wrapping tape lies flat on the shelf, sticky side up, all the way
across and under the belt and up on both sides, even extending beyond the belt
and up onto the back side of the shell, to help hold it in place.  (I am a bit
leery about applying the sticky tape directly to the shell, however, as it
might remove some of the shell's surface when pulled off some time later.)
 
We had very little luck sanding and filing the rough cut edges of the plastic,
and found that the tin snips did an easier, smoother job.
 
My husband (a confirmed non-sheller, alas!) suggests squirting some plastic
foam inside the plastic "base," between the shell and the shelf surface -- or
even some spackling (joint) compound -- to form-fit and support the shell even
better.  This would obscure the bottom edge of the shell a bit, of course.
And the foam is expensive, but a small amount ought to suffice.
 
I'd welcome any comments, modifications, or other tips, tricks and gadgets
that any of you might have.