Question about humidity in rack

I got a C-Serpents rack (V-70 tub) for my half yr old retic and I can’t get the humidity to go below 87%. It is dry inside, no condensation on tub walls, smaller diameter water bowl away from hot spot, using corrugated cardboard as substrate, and I already made a lot of holes on both sides. I do live in the DC area so it’s naturally a bit more humid compared to other parts of the country. The ambient humidity in the room of the rack is around 55%. Is this just how racks and tubs are, as in higher humidity and it’s normal? Thanks for any help!

I have an ARS 7030 open rack and am having the exact opposite issue. I am constantly battling to keep my humidity above 50% for my ball pythons even with no ventilation holes.