I've been thinking about it. Maybe you could try sprinkling some powder onto the bed and rubbing it in (if there is a slight odor). Perhaps the powder would absorb the odor?
Or OK, this is kinda funny but it wasn't at the time. Stay with me here:
When my daughter was around 12 or so (forget the age) her tennis shoes stunk and we thought it was her feet. My husband would take our girls to Children's Hospital in DC if they had the sniffles. So, he made and appointment to find out (swear to you) why her feel stunk (she was clean but her feet stunk).
So the Dr said, "Wash the tennis shoes". We'd been washing them but in a few days they stunk again! Then he said, "Take spray on deodorant and spray her feet. They are sweating and this is what is causing the odor".
We did and it helped. It wasn't long after that (insurance didn't pay for stinking feet...you can imagine the cost), that (for some reason) they no longer stunk.
Perhaps it was because we threw out her beloved tennis shoes (they were the keds kids wore back then (washable)). I guess the smell just got in there and wouldn't go away.
Are you guys laughing? Welcome to my world...you have no idea.
Anyway, finally my point. If they have an odor (it won't make them clean) but it might help the smell if you spray the foot bed with spray on deodorant. It probably won't hurt the foot bed. Not promising, but it's worth a try....maybe....