Asteroid belts are beloved by SF writers and readers alike. They are not the deadly jumble of rocks depicted in space opera. You could live on a rock out there and never have another rock come within visual range. The average separation of asteroids in the solar system is a million kilometers or so. So flitting about them requires serious delta-v for any kind of action oriented story. Putting along with an ion drive prospector will take a couple weeks. Fortunately with maneuver drives we avoid all that pesky rocketry stuff (even if we risk the ire of Chung and Burnside.)
Belters are the only career with a worse survival rate than Scouts. That should tell you something right there. Belters are also the only career besides Barbarians that take their families with them. I say that because unlike other saner professions you start as a Belter at age 14. I have nightmares about a 14 year old being allowed to drive let alone pilot a ship. There is a lot less to hit out there though. Roughly 1/4 of all belters die, strike it rich or quit after their first term going on to other jobs and adventuring. It is a way of life for very few. Less than 5% make it through four terms. Though by then they probably are in it for life. It is the only career with survival rolls modified by terms served (another example would be if you wrote up school teacher as a career.) Learning all the reflexes you need to survive takes time and practice and practice can kill you.
Some people eschew their family mining enterprises to join the Scouts. The Belters half mockingly refer to them as 'slackers.'
In fairness only the most competent young people are chosen to be Belters. This isn't going to ensure their survival. It's to make sure they don't take any other people out with themselves. The major problem with prospecting is other prospectors. Claims are jumped. Some friendly ships turn out to be pirates. Belters have few illusions about their survival chances a couple of AUs away from a habitable world. Boarding actions are fought to the death. More importantly they learn as they go on to avoid all contact on a mining expedition, often making mini-jumps within a system to confuse the trail of claim jumpers and killers. Getting a Belter to file a flight plan is like getting a mobsters to pay taxes. Belters don't pay taxes unless you make them.
Questioning a Belter's competence, courage or honesty is a quick way to a fight. People who are weak or inept endanger others. Saying this about another can damage their reputation and make work scarce fast or make potential crew members look elsewhere for a berth.
They have a strong apathy towards central government. It's fine for other people but of little value to them. In the Belt it's all on you and your crew. Very rarely someone may come along to help you out in a fix. Having a ground pounder in a suit 10 minutes away by radio tell you what to do or draw up ordinances for you to follow is not only silly, it may be fatal.
Out in the Belt there are no courts of law to enforce contracts or agreements. You stand on your word. Saying a man is a liar is another way to make him shunned and make him your enemy.
There are many kinds of Belters though they all will say they are the true Belters. Some prospect on moons. Some mine rare gases from jovian worlds. Others inhabit bodies in the Oort Cloud or reside on space stations. Generally all have the fierce independent streak and the 'you don't bother me and I won't bother you' mantra.
Another common trait of Belters is their ability to stay calm in a crisis. They'll panic as quick as the next guy if it's the better way to go. It seldom is. They also have a strong tendency to understate things. A Belter might refer to misjumping as taking a small detour or finding a 100 meter gold nugget as having a good day.
Belters teach evolution as follows:
Pirates> primordial ooze> monkeys> ground pounders> Marines> Navy> Merchants> Scouts> Belters> Rich Belters.
The only 'civilized' people they have regular dealings with is the Scout Service. The Navy seldom bothers with airless rocks. They protect worlds with tourist appeal who pay taxes mostly on time. If you get help from anyone it'll usually be a Scout. Scouts have a similar lifestyle and would make decent Belters if they didn't take on Government work (shudder.)
A Seeker is more than a ship to a Belter. Seekers are home for most of their enlisted lives and a good portion of their childhood as they learn on routine inner system runs and contract work. A Seeker is a means to earn your living, keep ahead of your troubles and see the universe. Seekers are almost never bought or sold, instead passed on from parents to children (or leased very reasonably.) They remain in operation for generations and no two are exactly alike. It gets to the point where Belters out in the cold dark can spot a pal's ship by its drive signature or the patches and welds on its hull.
As a final note, I'd give Belters two skills a term like the Scouts. I might even be inclined to give them a Danger Sense roll (something high like 11+) with a bonus equal to their survival bonus (thus a three term Belter would sense danger on an 8+ and a seven term Belter is no one to screw with.)