Aurora works pretty well for these, Avenger should be a good one although I haven't flown it since RECs broken. Done a pickup and delivery yesterday on live server using a Cutlass. Done it with the wife, she handled the package pickup and drop off and navigation, I was piloting. It took 1.5 hours, but the game didn't crash! Kinda amazing after all the previous iterations kept crashing every 10 minutes or so.
You can actually get boxes into the 300 series without having to land upside down, although it's not easy and requires some luck. The goal is to place the box on the wing so you can reach it by walking out onto it.
Stand behind the ship, to one side of the engine, behind the wing. The wing is too high up usually, so you probably won't be able to place it there. Instead of trying to place it on the wing, place the box on one of the engine's side panels that's right above the wing. On the 300i it's the one that is upside-down. Although your character can't actually reach that spot, as long as the box's blueish image is there, it will be placed there. (If you landed on an incline you might even have the chance to place the box right on the wing.)
So, the box will be placed on the upside-down panel, and it will fall onto the wing and stay there, for a while at least. Hurry up and get into the ship, open the bloody door that always closes automatically (just Open Door, don't click Exit ship) and walk outside onto the wing. Pick up the box and walk inside, put it down and you're done!
To get the box out, you can simply walk out the door with it (again, just Open the door, don't click Exit).
Worked for me so far, but the box can bug-out and refuse to stay in place, or just decide to drop through the planet at any point lol
I tried throwing it into the ship with the door open, but it always ended up in some weird spot behind me, so I wouldn't bother with that just yet.