We stayed at Lenny's place for Tomorrowland 2018. This was kind of a last minute trip, so we knew we were going to be limited on options as to where to stay and was nervous about having to stay in Antwerp as opposed to Boom, but Lenny's apartment was just perfect! It was walking distance from the train station (~10-15 min) in a safe area that was well lit at night to walk. For any future Tomorrowland travelers, the train is a super convenient way to get in and out of Boom from Antwerp and would highly recommend if you are not camping on site.
Although there is not a separate entrance for the loft, you do feel that it is your own place upstairs with your own private mini-kitchen, bathroom, and shower. With us arriving so late at night, we didn't really run into Lenny or her boyfriend at all during our short stay except when we checked in. She was super flexible seeing as how we were only in town for Tomorrowland and understood that often we would be back very late (3-4am).
The room was clean, the bed is a pull out couch, but it was plenty comfortable. She provided us with all the necessary linens and even provided towels and shampoo/body wash. It area is small, but it was perfect for just boyfriend and I. I think a third person would've fit, however certainly as just a sleeping arrangement.
All in all, it was a good experience. Lenny is professional and responsive and I would recommend!