Dark World is a destination though you cannot advertise your letter of mark.

A Tortuga/Port Royal pirate haven is an obvious must.

Perhaps the letter of mark is done through another star nation/colony for plausible deniability for Inner Reach? ie a noble on Clarion issues the letter of mark because his "duchty" has a unique legal distinction that makes his dutchy effectively soverign and separate from the Monarchy of Clarion like native americans reservations are autonomous. Thus the Dutchy is autonomous and rules itself but it cannot be effectively attacked by outer reach giving it a special legal standing.

Inner Reach does a quid pro quo or has a special treaty with the dutchy means that the Duke awards letters of mark  against Outer Reach and the UPF and Space Fleet cant do much about it. but the Royal Marines protect the sanctity of the planet Clarion thus effectively protecting the Duchty.

PCs are only the lattest crew of privateers to strap on their laser pistols and rocket against Outter Reach.

Edit: this is a militia type game but without any military discipline issues. Basically the militia played from the privateer side with quasi government sanction.

Make it late in the timeline and the privateer could be a decommissioned Osprey.

However, powers that be at Outer Reach will likely take a dim view of the fact that former milita vessels and former militia personnel are attackign their shipping and may lead them to make a move against Clarion in retaliation.

So maybe not a former militia ship unless we want a big pirate battle in White Light.

another take:

1. same back story Dutchy on Clarion in unique status of autonomous,

2. Duke has ties to Inner Reach and through some back channel dealings becomes the conduit for proactive sorting out of the Hive of Scum and Villiany at Outer Reach but in a way that allows the Inner Reach government and militia keeps its hands or psuedo-pods clean. ie letter of mark and privateers waging proxy war,

3. The cats paws of privateers have high mortality due to the inability of Inner Reach to come out in the open and support them thus Outer Reach ships can hound them out of the system since they must jump effect serious repairs or rearm. This leads to the latest strategem: a Q ship freighter and an all new PC dominated crew. NPC commander though (I have reasons- he lets you rail road the players with the Volturnus Survey mission 2 job)

4. ships name: Serenna Dawn.

Campaign arc is in Dramune where as a outward freighter they can dock at inner reach and do recieve clandestine support from Inner Reach militia: some material support: replacing expended munitions and intelligence reports etc. Adventure should build to a big blow up that even hits the Council of Worlds and the privateer Q ship must be disavowed- can no longer dock at Inner Reach and must lie low while the political situation plays out so the Duke has the ship go pure merchant for a time. And powers that be at Outer Reach have also put a price on the heads of the crew of the Serenna Dawn, making this ship a marked ship.

5. at cassidine its hired to transport expedition supplies and some Triad Institute of Technology specialist to Truane's Star for some Survey expedition. At Truane's Star spys for the local pirate ring the Star Devils spot the ship and a plot is laid.

6. At Volturnus the captured HS 3 survey ship of the First Volturnus Survey Mission lifts off to greet the Serenna Dawn claiming to have important data and were only just able to repair their ship for an attempt to get off planet. its a vrusk member of the original party communicating through a polyvox so there is no voice to compare to say Jamison or other members of the party and he states Jamison is dead. However it turns out the survey lander is loaded with star devil pirates and unfortunately its allowed to dock with the Serenna Dawn.

7. Enter Crash on Volturnus.

PCs are not the survey team but can run through most of the module and can have a "professor" NPC accompany them. They have an agenda: revenge against the pirates for the destruction of their ship and settle a score with the powers that be @ Outer reach for putting a price on their heads. When the return to the Frontier as heroes after the Battle of Volkos they get debriefed by Space Fleet who knows all about their privateer missions in Dramune and while they would have detained the PCs after the blow up of they caused in Dramune their actions at Volturnus kind of make it a wash so the truth about their activities in Dramune will be buried.

8. Returning to Clarion and the Duke who owes them some money, back pay and etc. (note the NPC ships commander is go by now maybe dead on Volturnus) After which the PCs are having a drink on Clarion Station and considering their options when the Duke's Major domo approaches them and interduces them to a freighter captain named Tylapper. It seems he's in desparate need of a crew and the PCs being old Dramune hands with experience dealing with pirates would be a good fit and just maybe the Dramune Run might be an opportunity to get a little pay back.