For any bike rack on the back of an RV (read: long distance from last axle to the receiver). Spend the 5 bucks at home depot on a ratchet strap and run it from one side of the bumper, loop around the top of the bike rack and secure to the other side of the bumper.
This will reduce the bounce and torque on the 90 degree angle weld of the bike rack.
Keep in mind, you still need to verify your 2" receiver is not just welded to said bumper and will rust and/or rip off. Ideally your rear hitch receiver will be secured to the frame in some way. If it's not, buy a rear hitch that mounts to the frame itself, not just the bumper.
The amount of swing/torque on that bike rack cannot be overstated; let your $5 ratchet strap rip/fray and replace it, instead of losing your bikes on the road.
Last note: if your bumper is not treated inside and you use it for stinky slinky storage, you're creating rust in there. (Note: no bumpers are treated on the inside.)