I made a simple sander to get to the bottom of hollow forms.
I took a spade bit extension and cut it down to about 6". I made a holder for the extension be drilling a piece of cold rolled and drilling/tapping for set screws, I made a second extension with a bent end. I can use any power sanding disk holder that will fit a 1/4" chuck. The handle is Poplar from the BORG.
(Mr Schlumpf and company, have me hooked on HF's.. Seems that's all I turn lately!)