boiled linseed oil can combust in crumpled up rags because the curing process is exothermic - it makes heat. So a crumpled pile of paper or rags might insulate it enough for the heat buildup to reach the ignition point and FWOOSH! It's also an oxidation reaction, so yes, keeping it sealed up tight will negate that issue.

I can't find anything about what specific plastics you can store boiled linseed oil in, just be aware of what solvents and siccatives are used in the specific brand you're getting and make sure that they're safe for polypropylene and you'll probably be fine. I'd recommend storing them on a metal tray and inspect the plastic before use, just in case. Also UV can cause chemical changes in the boiled linseed oil, so you'll want to store them inside something light-proof anyway.