It's true you can pry open the the cover. So that's limited security. But cars have been putting filters things in the line for years to keep hoses out and potatos or whatever else people might try to put down there.

Of course there are ways to get past these (I assume). But I don't know how.

I was told by someone who used to steal gas, that these are common in cars now. That it's very hard to get a hose into the tank.

Easier to steal out of motorcycles (without locking caps) and lawnmowers.

I just messaged a mechanic friend of mine to see what he says. I'll report back.