Night time incontinence. Need suggestions.

Cover mattress with plastic cover that surrounds entire mattress ( can find it at Walmart ).  Put adult pull ups on him.  Can also order a plastic pants like babies used to wear in The Day, but can't remember the company that makes these.  I'd Google this to see who makes them.  Can also put those incontinence pads over the sheets, or a "draw" sheet over the sheets with one of those pads in between the layers of the draw sheet.  Have a urinal close by in case he yanks the pull ups off.  Can also have a bedside commode nearby in case he needs to have a bowel movement in the night.  Maybe try parachute material and make him a pair of pants to cover the pull ups.

I've seen a few people here recommend the use of both an incontinence brief plus a rubber pant for night time use.
https://www.agingcare.com/products/waterproof-adult-pull-on-pants-449233.htm

Is he wearing adult incontinence briefs? If not, that might be a better option than plastic or rubber pants. Those would be very uncomfortable when filled with urine and wouldn’t stop the leaks. If he is and they’re still leaking, you might need to use overnight briefs.