I was a Seabee for 23 years and retired as a Chief Construction Electrician. And yes, it transitioned very well to the private sector. Someone like your friend would still have to go through a union’s program to become licensed, but could easily work in some of the trades without licensing. I went to work for a private U.S. company overseas that was contracted to the government. They didn’t care about licenses (or even qualifications in some cases).
As for getting into the Seabees, it could be a bit tight. The ratings (electrician, builder, utilitiesman (plumber), mechanic, equipment operator, steelworker, engineering aid (surveyor) are not what are called ‘critical ratings’ like the nuclear field and others, and I don’t know what the manning levels are right now. He should check with a local recruiter and see if what the availability is. If at all possible, he should try to negotiate a guarantee of assignment to Group 8 (Seabees) as a condition of his enlistment, or even a guarantee of a particular rating/school. If he has any construction skills, he should make sure that the recruiter knows about it, even if it was just working with his father as a helper.
Once he goes through ‘A’ school to learn his trade, he will either go to a Mobile Construction Battalion (MCB), which deploys overseas, or to a stateside public works or other entity that needs staffing. In a battalion, he will most likely be assigned to one of several companies: Alpha (mechanics/operators), Bravo (utilities), Charlie (carpenters, steelworkers) or Headquarters (surveyors and support staff). Overseas, he will work in his trade with a crew on various projects, but will also be called upon to help with other work, and will do his share of “shit work” like everyone else does. As he rises in rank, the shit jobs become fewer and the responsibilities increase.
Back in home port, it’s all about training, both professional and military, as Seabees are trained for defensive combat. That means qualifying on the rifle range, going on field exercises to simulate combat conditions, and going through endless readiness inspections.
By the end of a four-year enlistment, if he has kept his nose clean and done his job, he should be able to reach E-5, and will have experience in running a crew, planning out a job, etc., as well as a solid technical knowledge of his trade.