Oh I hear ya. It can be done and done well. I'm just thinking based on my experience that a 120 gallon would be tough. I used 40 breeders for a long time and had great success. I have advocated for glass plenty and still use glass, just small enclosures now.
I'm thinking a 120 with that footprint would likely need more than one lamp of different wattages to achieve a gradient, as well as multiple UTHs, also set to different temps. But I could definitely be wrong.

And had I known years ago what I know now I would have upgraded my larger enclosures years ago. They're literally a game changer.
I don't have a large collection by any means, but if I could I'd have gone all PVC by now except for my Hognose and KSB, but they're tiny.