Hello and welcome to just answer Dodge. Usually corrosion at the relay studs where the terminal connects is caused by excessive heat due to either excessive current draw from the heater grid, or a loose connection. This time replace the relay again, make sure that the eyelet on the wire that connects to the relay is clean and tight, and you may also want to consider replacing the heater grid under the intake plenum also. This is not a common problem that I see (although I have seen it in the past and it was due to loose connections at the relay). Another thing to consider is after you replace the relay/clean connections etc. apply some RTV silicone onto the relay studs where the wires connect. This will help seal that area and help protect it from further corrosion.
Hope this information helps. Let me know if you need more assistance with this.
You are welcome. Thank you for the accept.