Hi, Gina,
I had a senior bunny who became incontinent (could’t move back leg to hoist into his litter pan) at age 7. I found a site called Palace Pet Beds that sells cuttings of carpet that is used for puppies, geriatric pets and even in hospitals. It is a rug material that wicks away moisture so you just toss it into a washing machine and let it dry while putting down a fresh one that was washed the day before. It keeps your bunny from moving in soaked pee areas. It was work to wash often, but I loved them and could cut large pieces on sale into smaller sizes that fit my cage bottom.

You can sprinkle his bottom and feet with plain corn starch, which will also absorb the moisture on him, then dry him off and brush it off of him. I did very frequent (every other day?) butt baths. I put about an inch of warm water into the sink, held him in it, gently cleaned him with a washcloth and baby soap (uncscented) and towel dried him. He stayed still because it felt good, and he didn’t need his upper body or head cleaned at all, just the underside and feet that got soiled. Keep him warm right after – you can blow dry him for a few minutes on a low setting along with towel drying.

If he can get into the litter pan at all, maybe cut out the front and smooth the edges so he can have the entrance to the litter pan level with the ground, and let him move into the pan with litter if he likes that better.