All fair points. Note that they will be covered by the fitted inserts from TOYOTA, so not exposed to the sun. The trouble is that a bolt won’t thread into that hole on either side; the factory roof rack has a peg more or less that fits into that hole whereas all the other ones had bolts threaded into them.I would worry that the plastic will crack and get brittle in the sun, it will also shrink in the cold. It might work well today but I don't think that's a good long term fix if your goal is to just plug those holes. The rubber washers & bolts should be much more long term.