Fitting add on blinds to rear door
You just need to have the blinds cut to size, many home stores even big box can cut custom sizes. To avoid blind slap some blinds come with lower mounts that hold the bottom bar in place. This limits the blind to twisting them to horizontal for open or verticals for closed. 
Some higher end blinds actually have rails that contain the blind and bottom and keep it in place. And can be raised and lowered