How to Measure RV Window Shades for 2018 Grand Design 5th Wheel

Do not use an assumed rail-to-rail measurement as the order drop until the shade manufacturer and mechanism are identified. A 2018 Grand Design coach year and the description “room darkening pull down” do not establish the shade system or how its maker defines finished width and drop. The hanging position of the bottom pull rail can differ from the required finished shade or window-coverage dimension.

For an identified Irvine Slow-Rise system, the current manufacturer measuring guidance measures width inside the valance near the top, then subtracts 1 inch. It measures drop from the inside top of the valance or mounting position to the bottom of the window frame. That is a mounting/window-based measurement, not a generic instruction to include both metal rails. Use this method only if the installed system and replacement order are confirmed to follow that guide.

Irvine's pleated-shade guide instead adds 2 inches total to window width and drop, with shade width 1/2 inch less than the inside valance. That is a different identified shade type; do not apply it to an unidentified roller shade or treat the width addition as an automatic inch on each side for every outside mount.

Record the manufacturer/model or labels, mounting position and brackets, inside valance clearance, window width/height and the dimensions of the existing complete shade separately. Identify which dimensions the exact replacement's order form requests before submitting sizes. A steel tape and a second check help record measurements, but no measurement in this historical question confirms an order size, light-blocking coverage, fit or operating result.