Let's switch to physics, as it is really "force" we are talking about. Consider:
Motorhome > hitch > tow bars > baseplate > toad (this is the "system")
When all connected, you only have rolling resistance of the toad in complete neutral, however you achieve that with your particular model.
As you accelerate with the motorhome, force on the system will equate to the weight of the toad PLUS friction resistance from the tires/slope - maximum at first and then decreasing as things start rolling. This is why you have to install bars with weight ratings that exceed the weight of your toad. Too much and *bang* bars fail.
As you decelerate with the motorhome, again force on the system will equate to the weight of the toad MINUS friction resistance form the tires/slope. It is not more or less than moving forward, because the weights are the same on both vehicles and the interconnecting devices. This is just force in the opposite direction.
Of course force also has an acceleration component so if you floor the motorhome accelerator or slam on the brakes you increase force. This is why you have to install bars with weight ratings that exceed the weight of your toad and have tolerance built in for extra stress. The bars are ALWAYS rated at some lower percentage of maximum load for safety.
Now if you are buying all of that from me then you realize that when in towing configuration whether going forward or reverse the stresses are basically the same, just in opposite directions. You put just as much load on the bars when slowing down the motorhome as you do in backing up - actually much more when slowing down due to inertia of the toad and depending on your deceleration rate.
So what can you change here by changing from forward to reverse? Not the weight of the motorhome, not the weight of the toad, not the strength of the hitch, tow bars, or base plate. Basically the only thing you can (majorly) change is rolling resistance. And when you back up the only way rolling resistance can be increased if the steering tires turn the wrong way and bind.
Now we are back to geometry. Have someone in the toad keep the tires in the optimum position whilst backing up to reduce rolling resistance to minimum.
Okay, someone shoot some holes in it!
Note: I'm not including all of the calculations and variables, but the ones I am leaving out are mathematically insignificant (i.e. air resistance, etc.).
So if the tow bar manufacture says it will provide undue stress on the tow bars when backing up, then they need to prohibit you from decelerating and stopping as well. Once you get going you void your warranty by stopping, LOL!
Math and science, gotta love it.
PS Someone in the thread mentioned using the toad to pull the motorhome backwards (motorhome in neutral). NOW you are talking trouble as you've put the much heavier vehicle in the "rolling resistance" mode and this will change the force/stress on the hitch, bars, and base plate. Not to mention the engine torque on the toad as well. Would not recommend that at all. Remember this is all about the weights, what is in neutral (rolling resistance only), and which direction you go. If you wouldn't pull the motorhome behind the toad don't do it in the opposite direction either.