Using urethane
Put mast in place use small wedges to hold it
Wrap soft foam covered in vaseline around the base of the gap inside cabin to fill the gap ,remove once set .pour small amount first to check for leaks
Before you do this
Get some rubber sheet cut a circle about 6 in bigger than the mast cut tight mast dia hole in the middle ,slide this over the mast above the mast step ,once urethane set ,slide it down mast to cover urethane plug
To get the mast set
Fit a rope around the mast above the boom fitting fastern to the bow cleats
Fastern another rope above this take back to both winches . Tighten front rope put two weges in back 120 deg apart
Then pull back rope tight with both winches check mast set true using halyard to hand rail to measure both sides same put wedge in front.pour urethane
Lifting mast
Rope secured below boom fitting, then single half hitch just past half way with long tail to crane
Let mast ground then Lift it just off
twist mast to point correct way just before you let it completely ground
Once mast landed shake out hitch and let rope drop
Good luck
Bill