Working at a Union job in a non-union part of the US is it's own world that is unlike anything else in the working world. This has it's pros and cons. This applies strictly to the mechanical department.
Pros - Relaxed work environment. Anything required to make the job safe is provided on the spot. Great pay and benefits. Paid lunches.
Cons - Extremely poorly and vindictively managed at the top corporate levels. Union is at the same time supportive and own worst enemy in affecting any real change. Poor hours. Work holidays. No sick days. No PTO. Terrible vacation.
If you're single be prepared to miss the things that make life fun for at least the next 5 years and if you have a family be prepared to miss most of the important events of your families and kids lives for about the same time. There is 0 leniency and no PTO or sickdays to make this easier for the workers . Weekends? Forget they exist.
I'm not really sure who this job is most suited for the long term. If you're 45+, kids are grown and want a decently low stress, if dirty, career to retire in? Then I can see this being for you.
Despite what I typed above, at least as far as the mechanical department is concerned, it's not a bad place to work but it takes a special type of personality to work there til retirement. If you can stomach the heavy restrictions on your time and personal life, give it a try.