Be careful when stepping on the rear beam: because of the shape of the hulls, your weight plus the mast will make the boat "seat back" on the rear segment of the hulls and put you in a very scary situation... This is the reason why I havn´t been able to raise the mast solo myself (any advice for this?)
My mast has a home made base that is just a semi-sphere. It is obviously non captive, it requires to start a certain angle and to attach a safety line fron the base to the mast step. It won´t avoid the base to get out of the ball, but it will certainly avoid that I kill someone standing close to the base of the mast...