Metal darkroom trays ?? Advice needed

[Rick A]

You can fabricate a wooden box any size you need and coat the inside with Flex Seal. My new darkroom sink is made with it.
https://www.lowes.com/pd/Flex-Seal-L...B&gclsrc=aw.ds

[Drew Wiley]

Eric - trays have to be as long as wallpaper rolls are wide. Just do a search. They used to be available in four and five foot widths, maybe six feet too. Wallpaper is not as popular as it once was, but is still made, and no doubt trays too.
Rick - I'd want to do a little MSDS and tech research on anything like Flex Seal to see if there's any long terms risk of chemical contamination leaching out. There have been other alleged "waterproof" sealants that started breaking down over time in submersion. I'm not familiar with this particular product, but have heard BS claims many many many times before, and am particularly suspicious of TV ads. I use a certain hot solvent clear kraton copolymer sealer for that kind of application; but let it cure for a couple of weeks before immersion. Back when I sold such products, I rigorously tested every one of them. BS was more common than not unless a product was truly industrial and had long-term spec info. Home center products typically have some kind of "lifetime warranty" provided you return the original unopened can with purchase receipt in person to a specific office in a mideast war zone. Serious industrial products often give no warranty and rely on a proven reputation instead; they also have limited distribution.