If you're going to plan an ambush, you need to make it plausible that you're not sitting there in hiding. It's better if you can make it appear likely that you're not there, but plausible is almost good enough, to be honest. Nobody ever thinks someone is about to jump out and ambush them, so you don't really need to do too much to make the deception convincing, other than not be visible.
This is how it works in the real world. In a roleplaying game, of course, it's a good bet that the PCs are looking for ambushes behind every single door.
One way to spring an ambush on a PC group is to have one prepared, and wait for the first time that they let their guard down. As soon as they don't expect an ambush, spring it on them!
This will guarantee absolute paranoia for at least another two or three game sessions.
Commentary by Keybounce (who has not seen the movie)
Why would you abandon a "perfectly good ship"?
Well, first, did you? Will they find launched life pods? Any escape pods? The hyperspace modulator is dead. If the part is out, and there's clear signs of repair work, and missing escape pods, then the boarders might actually conclude that the people on-ship fled back to the planet.
But with all the escape pods intact and present? Then, you clearly had people working, and they did not leave. There should be no possible way that competent boarders will fail to detect that players are here.
So, a 50% chance that they are able to "escape" into the ship and try to accomplish something.
Now, what's the chance that they will be allowed to escape, and be followed? That does seem to be the standard mode of operation for The Empire/First Order.
Commentary by memnarch (who has not seen the movie)
Alright, so the mystery hyperdrive modulator allows the other ship to partially control this ship somehow. Definitely seems like the Imperial test was disrupted by this ship's faction or owner somehow. However, Conservation of Detail says to me that the First Order or the Former Rebellion was involved with the failed test somehow. Only problem is that I can't see how either of those groups would have benefitted from the test failing and wanting to leave the shipwrecks behind. The First Order does seem to be more likely though; the scenes with their equipment have used the most red lighting so far, so the color theming matches at least.
Unsurprising that BB-8's rather heavy, but I wonder if that's role-playing an injury or a simplification of the game mechanics for the comic. Finn is played by the best role-player in the group (Annie), so I can definitely see it as just extra flavor for the game. Simply rolling down inside or grappling down could damage the ship, so lowering down makes sense either way. It might be the ship of the party, but it is definitely not a perfectly good ship as Pete alludes to. Out of all of the jokes about its condition in Episodes IV and V, I can't believe I forgot about the biggest one where the hyperdrive actually blew up on camera. Held together with duct tape indeed.
Rey: Here, help BB-8 down.
BB-8: Oops. Are you okay?
Finn: Oof! Yeah, I wasn't using that clavicle anyway.
GM: The lights come back on and clanking sounds come from the loading bay.
[SFX]: Clank! ratta-ratta-ratta...
BB-8: Shouldn’t we lock the door?
Rey: If we lock it, they’ll know we’re in here. This way they might assume we abandoned ship.
Finn: Why would we abandon a perfectly good ship?
Rey: We wouldn’t, but have you seen this ship?