Dehydrate tomato slices cut thinly until they are crunchy and not soft. They will dehydrate quicker if cut very thin. I have also found that they could stick to the dehydrator racks so I brush a bit of olive oil (do not make areas wet). It really helps release the slices.
Put in either jars with perhaps 'Press and Seal' wrap over top before covering or vacuum seal. Vacuum sealing is best and store on your pantry shelf! Don't forget to label them. Bravo, you just made Powdered Tomatoes for Prepardedness or use in casseroles, spaghetti sauce, meats etc. Anything you would need tomato in and add spices accordingly. They will last a very long time-6-12 months, depending on how and where you store them.