U-bolts are the only thing holding your entire caravan onto the road. They bind your axle to your springs. Faulty U-Bolt installation can cause major problems with caravans when u-bolts are not checked for tighness..
Caravanning problems caused by stretching u-bolts can usually be easily fixed, however, unforeseen issues can have disastrous consequences. An example is the humble u bolt that clamps the spring to the axle. The bond between the spring and the axle prevents catastrophic events at high speed.