Although it's cheaper to have third party fire and theft, if you drive a more expensive van make a comprehensive policy may offer more protection for any damage to your vehicle.
You can reduce the risk of theft by parking off road in your driveway or garage,. Most insurers will offer up to a 5% discount if you do so.
Making a claim will not automatically lose you your no claims bonus. Most insurers will relegate you only two years meaning if you had 5 years no claims then you would still have 3 years.