It is probably unlikely you will find the outward bound passage of George and Rosetta since records are very few and far between before 1890.
I think you can assume, they sailed in 1889 for two reasons:-
a) their marriage was registered in the March quarter of 1889 at Newton Abbot District of Devon. This could have meant they either married in that quarter and year or they married in Oct/Nov/Dec 1888 and did not register the marriage until 1889. Either way, one assumes they were around to make that registration.
b) their first child being born in Chicago Ill. in November 1889.