Zarges (and Alu-Box) have been the go-to standard for decades. Lightweight, durable, waterproof and many are rated 'bear-proof'. Of course that comes with a matching price. But if you keep an eye out for surplus ones, they can be very reasonable. A guy had some for sale here on the Expo a year and a half ago that were 'surplus' from the US military (used for drone battery transport), Zarges K470, that were 1/3 the retail price and had the added benefit of killer foam padding inside for people that might be using them for camera equipment, etc. So keep an eye out on Craigslist, eBay, Marketplace for 'deals'.
They are fairly easy to modify due to their construction. I modified one to open from the end instead of the side for easy of access when three across on a rack.
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BTW - he is a great guy. He sold out of the ones he listed here, but it sounds like his boss gets a lot of them. Plus he is in you area (just south of LA) so if you want his contact info, PM me.