Sponge bath is ok but sometimes a good soak bath is better. Being very independent, occasionally, he finds himself stuck in the tub. I don't know how to assist him out. Weighing about 300lbs. & Do you know if there is rebath assistance for disabled patients on Medicare?
What does "rebath" mean? Are you asking if Medicare is going to pay for you to remodel your bathtub?
Medline Heavy Duty Shower Chair Bath Bench Without Back, Bariatric Bath Chair supports up to 550 lbs. It's cheap and you can have the shower running over him. It's not a soak but alas, in your predicament, compromises must be made.
This is one brand but there are several. Rehab centers and hospitals often use the same brand, but I don't remember the name of it now. They probably buy in bulk though.
https://www.walgreens.com/store/c/no-rinse-moisturizing-body-wash/ID=prod3946589-product
https://www.caregiverproducts.com/no-rinse-shampoo.html