Withm makes some good points, Catrin. Have you practiced mounting your tires such that you could fix a flat? The saddle bolt aside, changing a flat IMO is something you need to be able to do, especially for purposes of your brevet.

I also agree that a bottle of lube is a small price to pay for some additional comfort. While I get that it's not for everybody, it is often an effective way to prevent chafing and saddle sores.