The existing answers by Ken and Liam offer good advice. But unfortunately there is nothing you can do to prevent break ins. Thieves can be surprisingly stupid.
A friend of mine drove her jeep wrangler with a soft top to the trail head and parked it before going on a hike. The roof is canvas and the back side window unzips FROM THE OUTSIDE. She left the doors unlocked, so if someone felt a strong urge to rifle through her jeep they would not be inconvenienced and feel the need to damage the canvas top.
The thief did not even try the door, nor did they unzip the side window. They used a knife to slice through the back side window (plastic). Opened the (already unlocked) door from inside and rifled through the jeep finding nothing worthy of stealing.
No there is nothing you can do, to prevent breakins, even leaving the doors unlocked will not prevent a break in.
Image link of similar vehicle: Jeep Wrangler.