Aaron refuses to listen to Abe. He may hope that in building a large box, he can live beyond the current sphere of control. Getting sucked into a nearly infinite timeline can be quite annoying. Aaron may surmise that no matter what Abe(2) does, Abe(1) will still be able to create the fail-safe that Aaron(2) used to become his current existence. There is the danger that Abe or Aaron could get trapped into another long cycle of a feedback loop if they attempt to reuse the same boxes. Maybe Abe(1) and Aaron(1) will simply disappear from the current timeline. Of course, they are bound to make the same errors that their predecessors made.
Abe thinks it is possible to prevent the boys from creating the boxes again. Maybe this time Abe will get to go on a "two year, world-galloping vacation". Every time Abe(2) begins to interfere, Abe(1) should get more suspicious, more paranoid, and thus more secretive. Did Abe ever show this previously? Note how Abe and Aaron cover the garage windows. Watch the fountain scene again. Would you really expect to find a cat in a huge fountain of water? How would you react to waking up in your attic or locked in a closet? How would you feel if people saw you at a party, but you were never there?
A lot of people focus on the phrase, "this is gonna pass". Is there a dual effect such that if Abe invents a working box, then Abe(2) will come and dismantle it, preventing time travel, preventing his own existence? Then, without Abe(2), Abe(1) will be successful at building a working box, creating another Abe(2) who will come and dismantle it? Is Abe(2) only saying that he will do this to try to prevent Aaron(2) from leaving, knowing he will build a box with the knowledge he has gained? Abe was the one who said not to contact your double in the first place. We must first answer if they are permanent doubles or soon to be gone paradoxes.