Currently masks turn absolutely everything beneath them invisible including any background art you might be using on a vehicle. I’d like to suggest a “limit masking” checkbox within groups. And the default behaviour would be unchecked so as not to destroy anybodys previous work.
A group that has “limit masking” selected would be the last group affected by any masks within itself. But any group which has “limit masking” checked should still be affected by incoming masks that are outside and above that group.
So to be clear, you can still have multiple masks in multiple groups that affect everything beneath them down to the group where “limit masking” is applied. Then if you want to apply another mask to that entire group, or group of groups, just make sure it’s outside and above them.
Hopefully that makes sense!