Which dangerous defects can have occurred on a trailer with overrun brakes which has been parked for some time?

You answered correctly. If a trailer with overrun brakes has been parked for a long time, two main issues can occur: The brakes may stop working due to rust, especially if moisture has built up in the brake mechanism. Also, the cable connections can become defective over time from corrosion or lack of movement. Both problems can make the trailer unsafe to use. However, tyre pressure does not increase just from exposure to the sun while standing; in fact, over time, tyres usually lose pressure. Remember to always check the brakes and cable connections after a trailer has been parked for a while.