I would think that UV damage would be the most likely cause.
We have a 2024 310 RL(Weekend Warriors) and our seals are still in excellent shape.
I have treated them with rubber conditioner 2 or 3 times since we have owned it.
We also have slide toppers, so that certainly helps keep the sun off of the top wiper seal.
Given you are full timers, the constant sun exposure very well might have “dried” them out.
just my two cents. I've heard that these seals do not need any type of lubrication or spray onto them as the chemicals are already infused into the rubber when they are made. if they are cracked already then there's got to be a reason for it. possibly a bad batch of seals but I'm not sure of course. I think I saw a video from Josh. the RV nerd saying you really don't need to lubricate. these things may be able to search it off the internet. good luck! hope you can figure it out