Brake fluid is real nasty stuff and can ruin paint if spilled on it. Is the master cylinder cap loose ? I think it may be on the wrong side though.
Gasoline now contains alcohol. Any chance you had a gas leak ?
Is there any possibility that the starting battery is being overcharged and is outgassing abnormally ? Has it been overfilled with water ? You can have lots of 'splatter' from an overfilled battery when it is being charged. What does the underhood area look like ? Is there any indication that anything is attacking the paint under the hood or in the engine compartment? I know this is a stretch.
Is it possible that your truck got splattered by something that was spilled from a vehicle you were following ? Or maybe something that was spilled on the street and then kicked up onto your truck ?
But none of this would explain why an entire bed cover would get ruined.