The problem you are having is he's starting to see your bed as his territory. It could be that because you are washing yours and his scent off when you do the laundry, that he feels he has to rescent and reclaim the territory each time after you wash.
You can try having a litter box up there somewhere if you have the space, and that might be enough to divert the marking. Or maybe try bringing a blanket of his that has his scent all over it and put it up on your bed. If you use a scented laundry detergent, he might not like the strong smell and that could be why he feels he needs to remark it. If so try an unscented detergent(and unscented fabric softener if you use it) and see if that makes a difference. Then there is using a shower curtain to protect your bed if nothing else works to stop the behavior and you still want him to be able to come on there. Or you may have to reclaim the bed as your territory and kick him off for a while. Rabbits tend to like to pee on soft things and sometimes there is no way to get them to stop besides denying access.