Yup I made sure to do that
I simply put one of those dryer exhaust vents with the little flaps on the inside wall where the panel exhausts to prevent backflow of the air.
My renter said that it gets pretty toasty when the panel is going. The sensor is placed about halfway up the panel and set to turn on at 100 deg. F, so the bulk of the air is probably hotter than that. I haven't timed it, but on a good sunny day the blower comes on in about 15-20 second intervals.
I'd say it adds about 5 degrees in the apartment. I'm basing this off the temperature differential between this and the adjacent unit. The thermostat is located in the apartment with the panel, which unfortunately means the adjacent unit gets down to 64-65
... Guess I'll just have to build another panel! I'm wondering if it would be worthwhile to heat the basement with solar so it heats more evenly? :/