Home depot, Leows, and floor stores should carry vinyl extrusions (called industrial type) that are intended to fill the gaps between floors and carpets in industrial buildings - that might work if you can find large enough- fairly cheap and can be removed as needed. Another possibility- plastic extrusion intended to fill gaps between oven and counter or between washer and dryer sitting next to each other. If you have one high traffic area that you want to be safe- the pieces are usually not very long, but you may be able to find it in longer sections. Another option, a rubber or foam extrusion that looks like weather stripping, only larger- used for cushioning in gaps in industrial applications. There are so many types of extrusion out there for building applications, you should be able to find something if you are really concerned. We will be in deck building mode this winter, so this is something we are starting to have to think about ourselves. Had not thought about needing a gap for the winter cover, as I have not really seen any pictures of deck builds that show it- good to know about.
