Now that's funny... You'll hide it somewhere in the room in pieces where maids usually nose around, but you don't think the toilet tank is a good idea.
Actually the best place for it is probably inside the toilet tank. I've done that on two or three occasions and it's always been fine! Just make sure the toilet flushes ok and it doesn't interfere with the operation.
If you are just too paranoid about leaving your gun in hotel safe or toilet, then you probably won't be happy unless you leave the gun at home altogether.
I used to travel a lot. I've found lots of creative places. Toilet tank has served me well on a couple occasions. I also use Do Not Disturb sign a lot.