depends on what your concern is. the strap tension load isn't harming it at all (mostly internal forces), and the inertial force of the load in regular driving is more or less in line with what it would experience in a crash with somebody in the seat, except much lower load
there's a little bit of twisting on it when hitting bumps due to the unsupported middle of the boards, which is admittedly not great, but I'm not concerned at that at all because I pretty much never have passengers back there, so the chance of having a passenger, crashing in a way where this has been weakened enough to fail, and for it to fail in a way that makes it worse for the passenger is just not something I'm care about lol