The HL-LHC prototype crab-cavities are installed in the CERN SPS, which, for the first time, will allow for a comprehensive beam test with high energy protons. As the time available for experimental beam dynamics studies with the crab cavities installed in the machine will be limited, a very good preparation is required. One of the main concerns is the induced emittance growth, driven by phase amplitude jitter in the crab cavities. In this respect, several machine development (MD) studies were performed during the past years to quantify and characterize the long term emittance evolution of proton beams in the SPS. In these proceedings, the experimental observations from past years are summarized and the MD studies from 2016 and 2017 are presented.