Wayne,
from what you write, your mast appears to be deck stepped. That means it's about 4-5' shorter than mine (which is keel-stepped).
I tried to take some pictures, but they didn't turn out.
If you don't have a mast crutch in the back, you can make it from a length of 4x1 and a set of
transom pintles, the pin-like things you have on your rudder - except these are for mounting on a flat surface.
(While the rudder mounts edge on, the crutch would mount flat-side on).
You'll need 3/8" diameter to match the standard gudgeons on the DS.
(Should be easy to find a supplier via search).
All you do is drill 4 holes to mount the pintles and then notch the top end of the board to receive the mast.
To finish it off, I'd definitely suggest some varnish to weatherproof it and two small screws partially screwed into the narrow sides of the board. These would serve to attach a bungee that will make sure mast crutch and mast don't separate.
In the front, you could create some support that you can anchor in the tabernacle in place of your mast, or you could use a block of foam. The main thing is that the mast is raised fore and aft so that it doesn't rest on the cuddy.
If you raise it far enough in the back, you can put a tarp over the boat when not in use as in this picture:
[click on image to enlarge]For this a horizontal, or nearly horizontal mast works best.
You can kinda see the mast support in the back in the picture.
You do want to tie the mast to the boat in several places, so that it doesn't turn into a gigantic javelin when your car makes a sudden stop. It's a good idea to make sure whatever you use can hold at least 10 times the weight of the mast in the forward direction. Then you should be covered even in case of a crash. I always make sure that some straps go all the way around the mast, so that there's no conceivable way it can slide out under sudden deceleration.