Your question raises several more! First, I would recommend doing work to discover how animals are gaining entry to the building and prioritizing exclusion with unchewable, durable material such as hardware cloth secured with screws, sheet metal patches likewise secured, steel wool for small gaps around cables or pipes, etc. 
Are you encountering non-native, invasive rats, or are you referring to some species of native mammal, rodent- or otherwise? Species ID tells us critical info about diet, seasonal patterns, behaviors, climbing/digging abilities, etc., etc, and is really important for tool selection, whether traps, baits, or some other option. 
To address your immediate question, the trouble with baits is that they often do get stored and even if they're being consumed to a lethal dose by some animals, those animals are just as likely to die (and decompose) inside the structure as they are to be an easy target of some predator that would otherwise help with control, but then falls victim to the (secondary ingestion) poison. 
Further info about species ID will allow me to continue working on this with you to find some additional solutions, and/but exclusion needs to be job#1 or this will be an endless cycle of labor and expense for you :( 

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