I think that the PVC pipe by Tim is a good idea. Cheap! PVC comes in
all the diameters and lengths you can imagine. I would think that 3"
would do. Smaller is better. Seal one end with a plain cap. Seal
the other end with a "clean out" (http://www.bow-group.com/pages/
produits.aspx?LANG=EN&cat=58&pro=184) that has a screw top. You
probably don't even need to glue the parts together.

Then buy some metal U shaped hangers (typically in the electrical
conduit area http://www.drillspot.com/products/45...uit_Hanger?s=1)
to hang your new PVC container somewhere in the trailer. Finally, put
a towel inside so the probe doesn't rattle around and get damaged.

This requires a trip to the hardware store!!! Yoo-hoo. Remember my
motto - "Every new project deserves a new tool". ;-)

Now, Darryl, why is it that you need the spare probe? ;-)