25-30 min trade route worth almost 500k, safe.
On Planet New Tokyo, they sell engine components for 225 credits. On mactan base, they buy them for 1444 credits. Then, you can go to Leeds and buy Light Arms, sell them on Battleship Nagumo (In the Kyushu system), earning 463 credits per item. On Planet Kyushu, you can buy Niobium for 415 credits and sell it on Planet New Tokyo for 513. This takes 25-30 minutes in travel time, and the only time you're off of commercial trade lanes and jumpgates, is when you're going into and out from Mactan Base. This brings you to a profit of 1759 credits per cargo item, and using the dromedary, you will earn 483k. And I was hardly ever attacked, except in Mactan.
Alternatively, if you don't want to stop by Planet Leeds, Nagumo and Planet Kyushu, you can just buy gold at Mactan and sell at Planet New Tokyo with a 510 credit profit per item, earning 50 credits less per item but it'll be slightly faster. If you use a dromedary, you'll only make 14k less per trip.
I'm sure there are far better routes out there, just thought I'd share this one.
Take care.