Nothing wrong with Old School, especially when it works!
Another suggestion for you to use for a lid is the clear corrugated plastic sheets that are sold in lumberyards and home improvement places for use in greenhouse construction. A single sheet of this stuff is cheap, it's easily cut with tin snips or heavy shears and it weighs next to nothing. You can easily trim away slots and holes for things like HOB filters, heaters, feeding holes, whatever you want. It looks and feels flimsy, but I have lids made from this stuff that are years old and still good as new.
It has one huge advantage over eggcrate light diffuser material: it cuts evaporation way down. No need to top up water levels every day or two as you likely will be doing with eggcrate, especially during winter when the house is heated and the air is dry.
Thank! I've seen King of DIY use those before. I'll definitely look into it!