Dried tomatoes don't have to be "sundried" to be delicious. Where I live, the summers are too humid to dry foods in the sun (they just mold). That's why I opt for drying them in either a dehydrator or the oven. The result is just as intensely flavorful and colorful as the ones that were dried in less humid climates in the sun (and a whole lot less expensive).
Prepare the tomatoes for drying
Slice the tomatoes in half. For oval shapes such as pear or Roma tomatoes, slice them lengthwise (from stem end to bottom end). The slices should be no thicker than 1/4-inch. If they are thicker than that, further slice the halves into strips.
Spoon or squish out the seed gel and compost or discard it (or use it to make tomato water). This step greatly reduces the drying time.
Arrange the tomato pieces skin side down on racks placed on baking sheets. Leave space in between the tomato pieces on all sides.
Dry the tomatoes
Turn the oven on to its lowest setting, which is usually between 150F - 200F (no higher than 100C/Gas Mark 1). Let tomatoes dry until they are leathery to crisp, which can take anywhere from 6 to 10 hours. If your oven is hotter in some spots than others, turn the baking sheets around occasionally so that the tomatoes dry evenly.
When the tomatoes are dry, remove the baking trays from the oven and let the tomatoes cool at room temperature for 10 minutes. Transfer to airtight containers.
To use home-dried tomatoes, reconstitute them by covering them with boiling water and letting them soak for 15 minutes. Save the soaking liquid to use in sauces, soups, or pasta cooking water.
Paste or roma tomatoes work best for drying as they tend to be meatier and have fewer seeds than round salad tomatoes.
Dehydrated tomatoes will keep indefinitely if they are fully dried and then stored in airtight containers.
For ready-to-eat dried tomatoes like the ones in jars that you buy at the store, first reconstitute the tomatoes. Drain them well, then place them in clean, dry glass jars. Cover them with extra-virgin olive oil, pressing gently with the back of a spoon to release any air bubbles. Make sure the tomatoes are completely covered with the oil. Cover the jars tightly and store in the refrigerator.
Tomatoes dried in a dehydrator tend to have brighter color than those dried in an oven. To prevent tomatoes from darkening in the oven, make sure the temperature is no higher than 150F. If your oven doesn't go that low, prop the door of the oven open with the handle of a wooden spoon or a dishtowel.