Fanducts
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How will you later connect them as a single body? You can design as a single part and then cut to pieces for easy printing. Or design separate pieces with means to fit/connect them together.
Here is what I did with your file to ilustrate my method. Sketches were duplicated (without dependencies) from one body to the other and moved to proper places (changing attachment valued). I deleted the external geometry links first and fully constrained them before moving. Then changed internal contours to reference geometry and sweep to create outer solid. For ease of placement I duplicated the sketch inside the body, removed all geometry from it and Carboncopied the original sketch to link the dimensions to one sketch. Then created the substractive features to hollow the solid.