For a few bucks more, why not go with full square tubing instead of flatbar or c channel? Then use some cheap alumaweld brazing rods and a torch to cap the ends off so they're water tight. Then tap and drill holes on each of the ends of each bar to screw in some barbed fittings, and connect them all in a loop. It's 2024, and aluminum water cooling components are cheap af!
Of course you should cool off your components the best you can, IMO. I would rather WC the strips and drive the piss out of them at 100%.. if not overdrive them even more than that, and make 2 powerful lights that share one WC'ing reservoir\pump & loop, instead of one light with twice the strips.. and only be running them at 50%.. and still probably end up needing overpriced heatsinks anyway so they don't degrade too quickly. Go hard, not soft!