There are SO many anecdotal stories regarding rear bumpers and safety struts that it's difficult to know what to do. I'll try to cut down to the basics.
1) Your rear bumper is very flimsy and manufacturers recommend NOT attaching anything to it except for the spare tire.
2) Those safety struts do NOT add rigidity or strength to your bumper. They DO add an element of safety for WHEN your bumper fails. These only prevent your bumper from completely falling off. They don't prevent your bumper from cracking and breaking off at the welds.
3) There is another option to add a bike rack to the rear of your rig in the form of a receiver hitch that is bolted directly to the frame. You can find it HERE
. This is the only real way to carry things safely on the back of your clipper.
4) Many people will jump all over this and say that "you'll be fine, I've been doing it for years!" But it's only anecdotes.
5) That receiver hitch that I linked above didn't fit on my TT, so I fabricated my own to bolt directly to the frame and it's bombproof.