I stopped at KBMI at night once. And in the nearby slightly larger Peoria airport. Both in the summer.
Both of these airports have towers, but I'd say that KBMI gets the controllers who aren't good enough for a job at Peoria.
The guy in the KBMI tower seemed really not to be with it. After landing, and while taxiing, he gave me bad taxi directions which he then corrected, and then announced in a discouraging way that the airport would close in 15 minutes -- this caused me to ask 'say again' -- and he then decided to correct himself and say that the tower would close in 15 minutes. This guy seemed to say random incorrect stuff because he just didn't care - he was definitely not on the A-team of air traffic control, but at least he caused me no harm, with no other traffic around that night.
FBO at KBMI was comfy enough - pretty typical for a class D airport. It was open long hours, more than the tower. The FBO at Peoria was slightly better and open 24 hours. FBO attendants at both places were understandably pretty sleepy and bored late at night. When I pulled up at the FBO at KBMI I was sort-of-marshalled to a parking space by one sleepy guy, who then fueled me from a truck with a minimum of verbiage and eye contact, and I paid another sleepy guy at a desk. When I pulled up at the FBO at Peoria (also at night, you'll recall) there was nobody to marshall me and just one sleepy guy stretched out on a couch. Overall, both places will get the job done, but don't expect any joy and excitement when you arrive late at night.
You said you'd need a tie down and rental car -- I didn't try that, but I did notice that the hangar facilities at both KBMI and Peoria seemed to be sizable enough that you could probably park inside for the night if you want.
BTW, if you fly at night this time of year, it's really nice smooth flying around there -- the air is cool and still, the lights of multiple cities can be seen anywhere you might be, and it's just really pleasant night-time flying.
