Sean collects salvage for the Resistance at the edge of House Camp and keeps to himself. Once his wife was gone he turned to drink, and the bottle cost him his bond with Brian, his son. Brian has now vanished without explanation, Sean is coming apart, and he is hiding things that could be worse than they look. You will find him on the Promenade in House Camp.
As Brian's father, Sean is where the side quest Lost Connection begins: talk to him to start working out what happened to Brian. The main quest House Camp Flipper, part of the House Camp quest line, also opens with a visit to him and sets you to renovating the walls of House Camp. Over the course of these conversations Sean hands over Beer, Bucks, a Medkit AFAK and Sean's key, so it pays to return to him as each quest moves on.
Promenade (House Camp)
Beer
Bucks
Sean's key
Medkit AFAK