Off-premises cover is real and reduced
Most renters policies cover personal property anywhere, commonly at a percentage of the contents limit. That extension applies in a vehicle, at work, on a trip and across a border. It is one of the most useful parts of the policy and almost nobody is told it exists.
Property in a vehicle is a contents claim
Belongings taken from a car are covered by the renters policy rather than the auto policy, subject to the deductible. Where things are regularly carried in a vehicle, that deductible is worth choosing with the realistic loss in mind.
Recovering a loss abroad is harder in practice
The cover may extend and the practicalities do not. Police reports, documentation and valuation are all more difficult when a loss happens in another country. Keeping records and reporting promptly matters more, not less.