Hi friend, 
I thinking in how can do a split mould on to these motorcycle saddlebag, where I split... any help I will appreciate

Greetings from Chile

With respect - I disagree. How it was made originally from metal is largely irrelevant, that is a different process entirely. From what I can see in these pictures, there is nothing that makes it impossible to do as one piece. More difficult yes, but certainly not impossible. I've done several similar parts in a similar fashion, and have no doubt it can be done. At least going from these photos anyway, if there is something I can't see in the photos then that's another story.

Anyway, as I said before: one or two piece construction doesn't matter, it can still be a 3 piece mould which is what the topic question was asking.