Finally, the sleeve is in.
The rivet nuts M12 (3 x 3) will hopefully keep the mast in position before I use additional wedges once I fixed it with 9 M12 screws. The pressure will not be on the mast but I did cut lengthwise a tube 1000x 160x 5 in three pieces, that will be inserted into the sleeve.
For holiday reasons I had to.pause for four weeks (enjoying an invitation on a 60ft Sunreef katamaran) in Greece which with all her all inclusive luxury couldn't convince me to convert to this kind of sailing.
Korinth Canal is impressing though (also pricewise).