My rocker plate is a hard surface that catches most of the sweat that isn't evaporated by body heat and 2 fans. I wipe it down (along with my bike) after every ride and my shoes go on a boot dryer (and ozone generator) after every ride, so the smells don't build up like they would if my trainer was right on the carpet (harder to get all the sweat out). Mostly open plan basement (that doesn't get too humid) also helps (and gives me room to ride with a projector giving me a ~130" diagonal screen to ride in front of).
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"