WBCCI Numbers, Front or Back or Both?

I am not a member of WBCCI but will probably join at some point. I am more or less just doing my own family trips now.



I want to have my trailer name and home location done with vinyl lettering on the rear of my trailer, basically in the same spot the WBCCI numbers go. Is that a problem, if I join WBCCI later can I just put that number on the front?



Thanks