Welcome, Mac.
Since 2011 had a Roadster and now, since the end of 2014, a Plus 8.
I park in supermarket car parks, multi story car parks and at events and I have never locked either car.
I was advised never to lock the car with the hood up as the cost of repairing/replacing a slashed hood is far, far more than the value of anything inside the car. I leave a few things in the car, but nothing of any value.
When I have a case on the rack I do use a security strap and the soft bags behind the seat I secure to the roll bar with a small bicycle lock.
The storm cover is excellent for overnight parking as, Dave W says, you will know if it has been disturbed.
Morgans, for the most part, are not a car targeted by thieves as they are so conspicuous and relatively rare. I spoke to the people at Gott and Wynn and they told me that they have never had a claim for theft of a Morgan. Most claims are single vehicle accidents, and windscreens.