I'm sure it's been done - but it adds weight aloft (not good), could affect the bend characteristic, and if the mast does leak, you stand a good chance of trapping the water inside for good. It's really not that hard to seal up a mast so that it is largely watertight. It's probably less effort to seal up the mast than try to fill it with some sort of foam.
Last edited by Jake; 03/27/05 07:42 PM.