Welcome Hilooverlander,
The local home improvement big box stores (we used Menards) will cut shades for the window width. We wanted an inch or two overlap on both sides. Once the shades were mounted, we unrolled them 8 or 10 inches beyond the needed length, marked that point on the shade & cut them to that new length. Then unrolled the remainder of the shade, pulled the excess material off the roller tube and reattached the new custom length with 2 sided carpet tape. It took a little trial and error to get the tension right but not too hard. We removed the excess material so the shade diameter would fit easier between the walls when the Hi-Lo was down.
We went with roller shades cause our HiLo had leaks before we bought it and was mildewed and we didn't feel like cleaning our stinky, dirty blinds. Also we were going to Alaska and wanted to really block the light to get the inside quite dark for easier sleeping. We also velcroed shade material to the roof vent openings to block light there as well.
We used the readily available low profile metal shade mounting brackets so everything fit when the top went down.
I hope this helps & I haven't forgotten anything.
