Did the dinghy
actually improve airflow or did it cool by means of shading the deck? Before you go to a lot of trouble to construct some sort of tent, I'd suggest an experiment with cheap materials.
Materials you will need:
-- Two air thermometers
-- A cheap, light-colored tarpaulin
-- Around 10 tarp clips.
-- Some cheap line
1) Place a thermometer out of the sun in the V berth in late morning on a hot, sunny day and open the hatch
, Place the other outside the boat in shade.
2) Wait a half hour or so for the v-berth temperature to stabilize.
3) Take thermometer readings and record them along with the time.
4) Tie the tarp about bow pulpit height to your shrouds and forestay. Maybe tie it off to your bow pulpit as well to increase the width near the forepeak. Use the extra tarp clips to fold the loodr flaps up on top of the resulting surface and clip them in place so they don't hang down and don't blow around.
5) Wait an hour for the temperature to stabilize in the v berth and then read the thermometers again. Record the temperatures and the time.
6) Compute the two inside/outside temperature differences. Did the tarp help, or did it help enough to matter? In addition to noting the improvement, if any, how does the V berth feel subjectively? Is it more comfortable now? Keep in mind that the difference will become greater as you move south and Sun becomes stronger (i.e. the level of insolation will increase).
If the bow tent works for you, trim the cheap tarp to shape and use it as a template to cut canvas (in the long term, you won't like the rattly noise tarps make and neither will your neighbors) for your tent. I exepct you will also want to add some kind of pole in the center to keep the canvas from sagging and catching rainwater.
For the main cabin, also consider a boom tent. I experimented last Summer with a cheap tarp that covered the entire boom -- from the mast all the way to my bimini and it was great! I tied it off to my shrouds and the bimini framework. This year I am going to make one of canvas.
Obviously, neither tent can be used with sails deployed but they're great at anchor
or tied up.