If the overhang at each end is a concern, build a simple tray for the mast to reduce the cantilever. A pair of 2x6's on edge, with a 2x4 or 2x6 'ladder rung' at each end of it, layed flat underneath so the mast layes between the main members, glued and screwed (more than that, and you won't know which are actually supporting the mast), mounted to the bow rail with equal length fore and aft (wood) so it's balanced on its own and doesn't impart any load to the mast from it's own unbalance, with the mast nestled and firmly strapped in, will reduce or eliminate the bending stresses from the cantilever, depending on how long it is. Allow it to pivot on the bow rail, so you're not inducing any stresses by strapping it down.
Do the same at the stern, at the crutch or whatever the support structure is. In the middle, a simple short crutch will suffice.
If you do this right, the mast will be directly supported in 5 places, 2 at the bow, 2 at the stern, and one in the middle, with the bow and stern free to rotate where the wood meets the rail or crutch. The bow and stern ladder rung pairs will carry the same load, since the 'pivot' is at the midpoint. It doesn't have to be an actual pin pivot - it'll pivot well enough on the rail to equalize the load on each of the two rungs. It just shouldn't be a rigid moment connection to the boat. You're just trying to have roughly equal support load at two points separated by some distance in order to spread it out and reduce the cantilevered length.
It works sort of like the equalizer mechanism of a windshield wiper blade, though the center support is rigid, and has to be just the right length to not put bend into the mast.
Put a big red beehive light on the end of the mast or the wood support structure if travelling at night, the kind with the angle mounting bracket that you can get for $4 at any auto parts store, and you'll be legal in most states. Orient is so it's facing down, for all-around visibility.
Cheap and cheerful, and quite effective for breaking up the cantilevers and simple spans into small parts, so the bending stress at any point is quite small.
. Just strap it to the boat with equal amounts sticking out the front and rear. Don't forget to flag the rear is it's visable to semi's.
