I totally agree with Alozzy, even if the roof rack itself is aerodynamic, whatever you carry is going to greatly reduce that.
Thank you, Aloozy and jjeff. Let me just clarify on what you said : Do the roof racks themselves cause the drastic reduction or is it when they are loaded? I am glad to know to look for some that are aerodynamic. If the racks alone cause some reduction vs drastic reduction, it may not be a huge issue for me. I live on a small island (St. Croix) and since the 2018's get good range and I do very little highway driving, I may be able to live with some reduction.
I find the idea of a trailer very intriguing and since I'm no spring chicken, I like the ease of loading/unloading, but ... the cost! A workman recently ran over my SUP board so I have to replace it, too.