This is gonna seem off topic at first, but bear with me:
I vaguely recall a study that was focused on motorcycle collisions/fatalities/etc, trying to piece together common factors in an effort to steer production away from features that resulted in motorcyclists from being hurt or killed.
Color of the motorcycle was one of the things they looked at, thinking that harder to see colors would correlate with more collisions - after another vehicle would hit a motorcycle, the driver of that vehicle would commonly say things like "I didn't see him!" or "He just came out of nowhere!" so they figured visibility is a big factor. An unexpected finding was that white motorcycles were hit by other vehicles WAY less frequently than other colors, even compared to like neon orange and other super high visibility colors.
Turned out that not seeing the motorcycles wasn't really the issue, but a subconscious thing our brains do with threat assessment. Cars, trucks, etc on the road pose a mortal threat to each other, so our brain focuses on those automatically. Motorcycles... might get a nasty dent from hitting one, but that's about it, so relative to larger vehicles, your brain just doesn't give a fuck about motorcycles unless you're consciously thinking about them (so, takeaway from this post: make a habit to consciously think about motorcycles when doing things like changing lanes!)
White motorcycles were the exception because they looked enough like cops that they crossed that threat assessment line: running into someone who has the authority to take your freedom away is apparently enough for your subconscious to categorize it the same as things that could feasibly kill you if you run into them. (takeaway #2, of you're considering buying a motorcycle, maybe shoot for white)
So about the propane tank on the bicycle... if drivers think your bike has the potential to become a bomb, you bet your ass they're going to give you more space and respect than literally every other cyclist on the road.
It doesn't even have to be a propane tank, it just has to look like one. You could shape a chunk of styrofoam and slap an explosion warning sticker on it and get the same effect.
Shit, you could even make false propane tank saddle bags to give the other drivers a healthy bit of fear, while giving you a nice sealed container to stow all your crap in. There's potential here!