Paul
Something like a workmate would be ideal for clamping a keel but I would advise against doing this as when working on your boat you will be putting excessive lateral stress on the keel.
The keel could break under these loads and ruin your boat.
A better method is to use an old quilt or eiderdown, fold the quilt into a rectangle and use it as a soft support for the bottom of the entire hull.
But in my experience a custom made frame is the best way of fully supporting your boat whilst working on it.
I hope this helps with your problem
Paul
Edited By Paul T on 29/06/2020 14:15:08