I just went through this exact problem so I’ll share what I came up with. Basically I needed a pawn that becomes “based” in a ship that has an arbitrary and potentially changing location and rotation. Gravity needs to always be based on the ship’s orientation and the ships movement should not affect the physics of the pawn. Effectively it is Star Trek physics.
Cloning solution: I had the same idea of cloning ships, pawns, and all other world objects and basically moving the cloned world around each player while the ship stays stationary - giving the illusion of movement. I got this basically working but it involved a lot of complex transforms and it had a noticeable effect on performance. It could be done much faster by transforming the clones at a lower level in native code (believe it or not I only used Blueprint). However there are so many things to keep track of (juggling multiple virtual coordinate systems, lighting, etc.) that I realized this is not the best solution.
Physics scenes: It is possible with PhysX to have multiple physics scenes although UE4 isn’t setup to make this easy to do. If you put the time in to code the support it is probably the most elegant solution. However I decided to try a different route which involved less low-level coding.
Parenting and Relative Transforms: The solution I ended up with (which is working now) was simply to attach the pawn to the ship and use relative location and rotation updates to replicate the usual pawn physics. Unless you do the cloning solution you have to write your own pawn physics in order to support angled physics anyway. You have to track all of your own acceleration, velocity, and location updates as well as apply gravity but it’s pretty easy to do in relative coordinates and the attachment code handles inheriting all the ship movement seamlessly.
I should add that there are two ways to attach a pawn to an object… regular attachment and physics constraints. I can save you some time by not recommending your pawn be a physics object with a constraint. Constraints are springy attachments and even if you jack up the strength on the constraint it is going to jiggle around or drift if your ship is moving a lot. Regular attachments don’t have this problem. I had hoped to use physics because it would be nice to just “apply force” to simulate gravity but real physics just can’t eliminate the effects of the base platform moving no matter what you try.