This duct is like headers for your RV roof top air conditioner. There is a commercial product called RV Airflow that you can buy should this print be too difficult. They have great youTube installation videos so you can see how it works. I included the .stl files that should fit a 2018 Winnebago Vista 29VE or similar with the single Coleman Mach 15 air conditioner. There is an offset between the down vent from the AC and the outlets that can be adjusted in the OpenSCAD files. At the top of each OpenSCAD file you can assign a 1 / 0 to select the variables straight or curved segment or both to see how they fit together. The left and right were assuming I was facing the back of the RV. Dumb, I know. The pieces fit into the ducts well enough that no seal is required. Simply install and use aluminum tape to join the two pieces on each side. Wrap the tape half way around the straight piece and install that first. If you're good with OpenSCAD you could add flanges at the mating surfaces. I recommend ABS, but try what you have. This duct eliminates the white plastic sheet that is between the ceiling and the outer vent cover. Block the sliding "dump" vents in the vent cover. The airflow out of the ducts is about double what it was before I installed these ducts. I also cut out every other segment of the back outdoor grill to improve airflow of the coils outside. I now have about twice the cooling BTUs of the stock unit. Each OpenSCAD file will draw both the straight and curved segments, just set the values of the variables straight and curved on lines 4 and 5 to enable each segment.