Caravans and mobile homes have their own section in the regs. One of the reasons you have a CU is so you can have lower rated wiring (saves weight and cost) and the ceeform connectors can still carry higher than 13amp. Useful if you're powering more demanding loads like an oven or aircon.
For example, this is how caravans are powered, and extension lead to a CU in the caravan. Are they notifiable?