This is far from ideal use of a diesel with a DPF. Precautions you can take are to change the engine oil and filter every 7000 miles. Take the car on as many distance runs as you possibly can. Whenever you stop the car, open the driver's door. If you are aware of heat under the car, that is the DPF actively regenerating and you need to drive the car for another 5 - 10 miles to ensure regeneration is completed. if you don't, fuel injected into the engine to promote regeneration will sink into the sump oil, contaminating it. Check the cold engine oil level regularly, at least every week, and if you notice it starting to rise you need to get the oil and filter changed.