Well having the same issues with call signs, (K8FC living in Colorado) what I did for CO QSO party was to sign "K8FC/FRE" on cw. I did not operate SSB so have no personal experience. But when I calle
COQP with K8FC/FRE or K8FC/CUS Perhaps the folks who go mobile in QSO parties could comment, but I have always signed plain old N9RV from Montana because I have thought that LOTW would require a sep