Is there any air moving near/across it? Like I mentioned, I've got a small fan moving air across my Lumatek. In a stagnent air environment it gets pretty hot after maybe an hour. But just a little bit of air movement makes a big difference. I put my fan (pc fan) on a speed controller to see how much air flow it needed to stay cool. It doesn't take much. I can turn the fan way down and it can still keep the temps pretty reasonable. I'd bet even just getting a little air movement from a nearby fan who's job is really to circulate air for something else would be satisfactory for me.
Good luck with the second unit.