One of my previous cats used to get so stressed in a carrier that he would pee in it. Then, he'd have to get a bath afterwards, making the whole situation even worse for him and us. My partner did some research and bought a couple of soft sided carriers that didn't look at all like hard ones the cat was used to. We unzipped all the sides, decked them out in blankets that smelled like our cat and then liberally sprinkled them with treats. Within a couple of days, our cat had come to think of these as cat houses instead of carriers. When he needed to be zipped up in it, he was docile and willing. He thought of it as a safe space, and it helped lower his stress levels when he was taken outside the house in it. Those carriers are now constantly in use as cat houses in our home. It was truly one of the best cat tricks I ever learned!