Oh my, I'm sorry, that must be really hard to deal with for both you and your cat. One of my cats has blocked twice, and one of my biggest fears is that it'll happen again despite doing the all the right things to prevent it.
It must be really frustrating... it sounds like you feed only wet food, and with added water even, so getting enough water is not the issue. You feed a high quality high protein food along with the prescription food, 3 times a day...no dry food right? You could try going raw again, or the other option is to feed only the canned C/D and see if that works. C/D is pretty sub par when it comes to ingredients, and its expensive for sure, but if it does the job and keeps your cat from blocking, well that's the most important thing. Did the vet find crystals in his urine all three times?
You probably already know this, but FLUTD is not just diet related but can be stress related as well. I use Feliway plugins to help reduce the stress levels of my cats. Some people don't have much luck with it, but I find that my cats do seem more relaxed. They fight less, and it also helps to curb Sadie's over-grooming habit.
I've also learned to be careful about changes in their environment and routine. The last time Cheddar blocked, during his recovery, my displaced sister and her two babies were staying with me for about a week, and having them here stressed Cheddar out enough that he started showing symptoms again.
It's also really important to keep the litter box very clean so they don't have any reason to hold their urine. Cleaning the box frequently also gives you a better chance of noticing and catching a problem early. Know the signs... small clumps of urine and frequent trips to the box, licking his genitals frequently, any sign of pain. Cheddar even kneads blankets and other soft things frequently when having problems, probably due to the irritation.
After three blockages, though, I think it's time to consider PU surgery. It's a complicated and expensive surgery, and although it won't solve the underlying issues, it will greatly reduce the chances of developing a life threatening blockage. For cats that have a history of blocking, it's often the best option.