Been using it for 10 years - no problems. I do not fill completely, but still about 4.5 gal ea. Bumper handles the weight just fine.
Not concerned about a rear-ender. That would be the problem of anyone following too close and not paying attention.
Keep in mind guys that I am carrying empty containers to hold grey and black water. The weight should be under 20 lbs total. They are bulky and I would like not to have to carry them in the pop up living space.