Our OSI 20 is very similar to a Hofbauer 20.  They are virtually
identical to the casual viewer.  The bottom of the case has a sheet
of plywood or fiberboard fastened to it to protect the pipework.
It is pretty firmly fastened in place with screws.

We have a home-made box cart for our organ.  I run a ratchet and belt
tie-down (without hooks) over the baseboard (under the organ casework)
and then down under the cart and back and tighten it.  It has worked
well.

The hookless tiedowns are sold as band-clamps for woodworking.  You
could modify the hook and strap type by cutting off the hooks and
either sewing or tying the ends together.

Wallace Venable