Caravan and trailer tyres fail on age and heat fatigue far more often than on visible wear - check yours against real-world industry replacement guidance.
Based on industry guidance (Tyre and Rubber Association of Australia and major manufacturers): caravan/trailer tyres should be replaced at 5-7 years from manufacture regardless of tread, because they flex-fatigue and heat-degrade over time even with light use, and often see long idle periods in the sun that ordinary car tyres don't. The legal minimum tread depth in Australia is 1.5mm across the tyre. This tool gives a planning guide only - always have tyres physically inspected by a tyre professional for cracking, bulging or uneven wear before a long trip, and check your specific tyre manufacturer's guidance.