Here's the problem. The forces created by heavier suspensions and increased distance from the axels to the hitch receiver found on travel trailers can create a much harsher environment than a regular passenger vehicle. Read that as more shaking and "whipping" (up and down action) putting a heavy torque load on the angle brackets, bolts, etcetera. RV rated means the manufacture has tested the rack to stand up to the additional pounding the rack will take without failure and will stand behind it.
I use the Yakima LongHaul, which is a new rack. I had purchased a Yakima Dr. Tray, which holds 2 bikes and will tilt down for easy loading/unloading. Price about $500. I was contacted by Yakima after posting a positive review where I mentioned it was for the back of our TT. Yakima contacted me and recommended I go with the LongHaul due to it's RV rating. They arranged for me to return the Dr. Tray for a full refund and I went with the LongHaul $300. There has to be something when a company wants you to return a more expensive item and recommends a less expensive model.
The LongHaul is a bike rack designed, built, and thoroughly tested to stand up to the long miles and rigorous demands of RV and travel-trailer use. Durable, stable and secure, the LongHaul carries four bikes with ease in the SuperCush ZipStrip™ cradles. The LongHaul is easy on and off, includes folding arms and a built-in bottle opener. Exceptional security is built in with a full SKS security package (built in steel cable) that locks your bikes to the rack and the rack to the vehicle plus a lock for the hitch pin. Both locks are key matched. Holds up to four bikes.
Then there's the issue of mounting. The square, hollow 4 inch bumper on the back of most units and it's mounting brackets are rated for about 100 pounds (that is from Jayco). It's made of thin steel and not a structural support. Figure your spare, if mounted on it, comes in at about 50lb, the bumper weighs maybe 10-15 lbs, for a total of 65 pounds. The mounting brackets for the bumper are relatively light steel and probably welded to the frame (mine where). So while towing with a bike rack plus any bikes, the bumper is subject to torque, and can twist when the rack is bouncing, even when not carrying any bikes.
A decent rack weights at least 25 pounds, so you overload the bumper with anything more than an all plastic trike. Check out this video of someone who worked on a bumper that broke down:
I've beefed up the mounting with a second set of brackets rated at 500lbs to support the spare, the rack and 2 bikes. These brackets fit tight around the bumper, allowing no twisting and are bolted to the main I-beams of the trailer frame. Since adding the brackets and the RV rated rack, we've been able to verify the rack doesn't bounce anywhere near as much, the rack has no torque when it does bounce and is solid. Plus the bikes aren't getting whipped around (that torque thing again) anywhere near as much as they had before. And when we haul bikes on the back of pickup, we don't feel it whipping and shaking like another we had used.
One last thing to add, no insurance company I've been in contact with (RV, auto, home) will cover the damage or lose due to overloading the rear bumper or the damage/lose of any bikes that where being carried on an overloaded bumper.
