Freddy, there was rain predicted all day yesterday (which we haven’t gotten in forever). A simple check of my weather app avoided that situation yesterday. An enclosed trailer helps that, but if you are at the track and it is raining the kart is already wet.
I also have a cover for my kart. If it is foggy or light rain, it works well. I also have a large tarp for my trailer in case it does rain, it’s pretty easy to throw over. Sure an enclosed trailer is nice, but absolutely NOT a necessity for this sport.