A barge should be roleplayed as a base. Immobile. Or hardly mobile.
When trading, it is a huge target, not only for real pirates, but also for OORP lulz piracy where people post threads like "I killed a barge!" afterwards (can you remember? We had that).
If I were a pirate, I would not attack a barge simply because of its size but that's different in FL, as defending a target is never possible. So attackers really don't have to fear anything.
Thus: take your 5k, split the risk, use the barge as a base for RP and don't be a target for lulzers.