Want to put a rear storage rack on my S-TX DX 137

[Cabinflyer]

My S-TX DX 137 has two saddle bags and a small rear bag. I want to take a 3 day trip into Canada from Minnesota, and need some extra storage. My rear bumper has 4 holes for mounting a 2-up seat. My old 2014 AC Crosstour had a rack on it, and I think it uses the same setup. Are the Yamaha and AC rear bumpers the same? OR....does anybody have ideas what I could mount on so I can keep the current bag setup??

THANKS!!!