Heat means resistance - the only thing getting hot should be your coil. Speaking of which, you don't mention the resistance of your coil. If you're sub-ohming you could be exceeding the power rating of your switch (never a good idea). The heat of your tube is probably just it acting as a heat-sink for your switch since solid metal tubes rarely have enough resistance to get hot directly from typical power flow in a vaping device (and you would probably have battery problems long before the tube would get hot).
This is definitely something I would take care of immediately.
The statement that your switch gets hot means it isn't a good switch (it has too much resistance and may be getting ready to fail). If a switch fails with a short it could cause a catastrophic event (ie pain and/or damage). If your battery isn't getting hot then its probably not a shorted switch now, but heat is still a problem. Remember that your Li-ion batteries are vulnerable to heat and if they get too hot they vent hot gasses - no one wants to play hot-potato with a device held next to their face that generates thousands of degrees of plasma. I am super careful with my vaping equipment.
I changed to variable wattage devices from mech mods to get another layer of safety. I also changed to IMR batteries from ICR. Lithium manganese chemistry is safer than lithium cobalt - lower resistance and thus lower heat generated when used (charged/discharged).