The trick with drying tomatoes is to get it done quickly, if it takes time moulds and yeasts will develop. Take out the seeds as they have liquid around them, you can add salt, drying in the car or van is a good idea it works, you can wash them in camden tablet solution this slows down mould. They need to be done in two days maximum.
Also plum tomatoes are the best as they have little liquid to start with.
Stored in jars with herbs is well worth it, great later in the winter.