The Vista LX product wasn't released until 2016 model year. I'm guessing you have a 2016 but because the chassis was manufactured in 2015 you are describing it as such. Check the placard on the wall next to the driver's seat. You should see it is actually a 2016.
There are wiring diagrams available online - but there are two for the 2016 Vista LX 27N (none for the 2015 because it didn't exist). This means they made some changes mid-year. You can tell which is correct for your RV based on the Serial Number (not the VIN). Again, you'll find the serial number on that placard mentioned above.
Here are the links to the two wiring diagrams:
27N(Serial Number begins with 10E38U1)
https://www.winnebago.com/Files/File..._e27n_wire.htm
27N(Serial Number begins with 10E38U2)
https://www.winnebago.com/Files/File..._e27n_wire.htm
Usually the chassis is grounded near the batteries under the middle stair in the stair well.