I use the spray can cap to keep stuff out of the filler neck ABOVE the flap/valve. Once the debris is into the recess above the flap/valve, there's no keeping it out of the tank when you open the flap/valve with a pump filler head neck. I do the same on my Ford Transit which has no cap.
I dont like how you cant use a locking gas cap option, anyone can pop the door open and vandalize my fuel inlet. Also when fueling, I notice when I go get gas, I have to mess with the fuel pump nozzle to get it to lock on the handle, not all the way in, more like 2/3rds in. is it me?