Marlee was my hardest to litterbox train. We removed all bedding except in the litterbox when she went from a cage to an xl dog crate and gave her hay mats and a fleece blanket — she peed on both and would lay on the plastic floor of the crate. I felt bad, but took everything out except the litterbox. It took two days and a few “litterbox talks” but she got the message and got her hay mats and fleece back. Marlee and Moshi now live in a large 3-xpen area with fleece covering the entire floor. We still get the occasional stray poop and the few poops that get kicked out of the litterbox, but pee is always in the litterbox unless there’s something wrong (she just got over a UTI and the pee dribbles were the “sign”).
Like the others said, bedding only goes in the litterbox. You could provide hay mats to sleep on until he gets the message. Make sure to put some of his poops in the litterbox and let him see you do it. If he pees outside the litterbox, wipe it up with a paper towel and put that in the litterbox too. Ince he gets the message, pooping everywhere should significantly improve, but you may still have a few random poops around — sometimes they just need to mark, and sometimes one just “falls out”.