Mine are very comfy but came with the Cali already fitted. I assume not easy to fit as they fit so well. The manufacturer are California Camping but are around £600 which is mega expensive for some seat covers
I don’t think any of the good ones will be an easy fit but once on you probably won’t be taking them off. There is a YouTube video where a couple (a bus and beyond) fit some one their Cali and it take around 4 hours. They look great and if I didn’t have them fitted I would get them