It is easier to recaulk while the current caulk is still good as it allows you to simply clean the area with alcohol and caulk over the existing caulk. If the existing caulk has already started to chalk and break down you will need to completely remove the old caulk before applying the new.
Window Weatherstrip Shrinkage
Overtime the weatherstrips will start to shrink due to age, temperature, sun exposure and normal wear & tear. With a little maintenance you can extend the life of the weatherstrip before having to replace them.
Maintenance: Be sure to keep the weatherstrip clean and coated with a good rubber protectant. This will protect them from the elements and help keep them from shrinking. If for some reason they do shrink you can attempt to stretch the seal back out to the needed length. You can move the seal down the window as the most important part of its job is to deflect rain water from the water track of the window. Note, by moving the seal down and placing the gap at the top of the window track can cause cold air to penetrate the interior of the camper more easily.