If I could manage, I think a layer of glass on the inside and some lightweight filler would be my preferred method. Might be a bit tricky as you would have to do it in two operations, first do the glass, then glue the glass in position and add the filler. I would hate to add weight and glass to a carbon Tornado mast!
Sad to hear that your Marstrøm Tornado mast leaks due to what sounds like a poor solution. This is something the technical comitte of the ITA should adress.

We sealed Paulw's mast with epoxy foam.

I don't think any sort of foam can handle water pressures as the mast goes under. Even a full sealed mast may have to take a huge pressure if the boat pitch poles and goes nearly full turtle before the bouyancy brings it back up.