After I can not find any source how one can prevent that raccoons enter the rabbit enclosure, I turned my point of view:
What let pet raccoons stay in their own enclosure?
(If they can not get out, they would not get in is my thinking)
To this Question there are a lots of sources, I will give a resume:
The grid should be stable, for example "10x10 dog kennel chain link fence"  or "Wire should be 1"X2" welded wire" 
Doors should be difficult to open, i.e. "Raccoons have almost human-like hands where they can open cupboards and refrigerators" 
They can scratch trough wooden board: "If they want in bad enough, they will scratch the door and carpet. If you are concerned about your doors, you can put some kick plates on the bottom of the door. This will prevent the raccoon from scratching any holes in the door." 
What I will change at my rabbit enclosure:
In my Question I linked how my enclosure today is build.
I will add:
padlocks at the stable doors, until today there are wooden lock bars (wooden bar screwed at the frame). Same thing at the hutch roof (able to open to clean inside).
I use proper wire yet, but I can improve the binding of it to the wooden frames. As I build it I bond the wire with a little stapler to the wood, but now I think I should screw it or at least nail it together.
I want to anchoring the enclosure better on the ground, so it can not be lifted. I have no estimation how much power raccoons have, so I have to assume, they may do it.
I will check the wood daily for scratches. New wood will be thick or covered with some "scratch protection" like the mentioned metal plate.
 Care Sheet For Racoons