On the Gen 1 Slingshots (2015 -- 2019) with the GM motor the exhaust came out just below the passenger seat and pointed out a little so there were some fumes possible when not moving or moving very slow. Then depending on lots of other factors you could get a little fumes in the cockpit. It's an open vechiel and when driving in the country past a 'hog' farm you can get the smell of the country in the cockpit. Or not moving and sitting in traffic on a very hot day --- little warm in the cockpit.
my exhaust on my 2016 is still factory stock and usually if I get any exhaust smell they are from other vehicles that are around me when stopped. Never had any noticeable issues from my own exhaust