Tateyama City: Located very south of Boso peninsular, Chiba prefecture.
The venue Tateyama Resort Hotel is 10km further south from Tatayama railway station.
There are public direct buses available between Hanada airport and Tateyama station. The bus schedule you can find in Haneda Airport - Kimitsu | Haneda Airport Limousine | Keihin Kyuko Bus (hnd-bus.com). The transportation between railway station and Hotel is provided by hotel shuttle bus (need reservation).
The public transportation between Narita airport and Tateyama is less convenient. Easier rout is go to Tokyo station and take direct bus to Tateyama station. The workshop plans to arrange a bus in the Sunday evening to pick you up at Narita airport.
Tateyama Resort Hotel: 館山リゾートホテル【公式/最安値】｜南房総の海と温泉とコテージと (tateyama-resort.com) japanese page