Try the sheepskin. It should wick the wet away from his body and you can wash it. He may not be able at this point to even use a litterbox no matter what you try.
There is a company called Palace Pets and they have very nice “beds” that can work – they are pretty good. You can also look in the dog section at the crates and they have something that you can use for fleece as well.
I have a rabbit who has arthritis and he’s terrible with his litter box – he sometimes gets in it but I’m not hoping at this point he will ever be even 10% at using his box but since he’s not disabled like some of my past rabbits I use a few washable rugs with plastic backing and wash weekly and air dry.
No matter what you try, you are going to be challenged and possibly frustrated because you feel like you just cannot keep them fresh and clean but try not to get too frustrated if you can…I know sometimes I feel upset because I don’t feel like I’m giving the absolute best care but I know I’m doing the best I can.