I am sure those nails will rust which is a heavy metal I'm the tank which rays sense. I wonder is the heaters will heat soak in to the wood? Nice solution though if it works.
I agree with t1, just buy a guard but more than that, get a sump and 90 gals is a short term tank, 6 months max therefore design the next tank with a sump or inline heaters. Rays are a big money commitment.