The ash would be treated with a por 15 base coat and then a coat of quality exterior black paint as i'm after the black bed wood look . Truck will some elements but will be parked indoors when not in use .
Ash always treated me well as far as hockey sticks go
If that is your plan, I think it would be fine. It is actually cool to capture some soon to be rare wood species in an antique vehicle. I used white ash for the troop seats on my 41.
