Caulking the 'spoiler'

We have had at least one rpod owned by someone on this forum where the frame failed at the axle location. So they can break, no question. I've done the stress calcs and I'll be generous and say that the frames are not over engineered.  If you were to assume that anywhere aft of the axle was equally good to place load, with no regard for the distance to the axle, then that would certainly exacerbate the likelihood of that kind of failure happening. That's pretty obvious, and most owners know not to hang heavy stuff way out there. 

LA, you have done the smart and prudent thing and measured your tongue and trailer weight accurately, one time. Once you have done that there isn't any need to repeat the process unless you make significant changes to your trailer or its loading. Barring coming across those gold bars camping in the CA gold country sometime your loading for the next trip isn't going to be much different from the last one. I don't check mine each time either. 

Its the same with flying, the FAA says you are supposed to do a weight and balance calc every time you fly but if you are loaded with the same ppl and stuff in the same seats and places there is no reason other than regulations. So pilots don't do it. They at most just keep the same w&b sheet in the plane so they can show it to the FAA inspector if they get ramp checked. 

I know for sure that some of the semis roll along I81 here at well over 80 because they handily pass me in my Prius while I'm cruising in the high 70's. Not all, but many do. I81 has more tractor trailer rigs than street cars on it most of the time. If your fore/aft trailer balance is good you will get a very noticeable buffet but not a wag. 

My guess is that the spoiler does a little to reduce drag but it would need to be larger to be really effective. Someone correct me if I'm wrong but I believe it is larger on the newer rpods. 

When I did the stress calc on it I assumed uniform loading in the trailer and 3500 lbs axle load and got a safety factor of less than 2. That's really not enough considering bump loading. Really it could happen to any of us if we were heavily loaded and hit a good big pothole, especially if that load was hanging off the rear bumper and not uniformly distributed. 

It looks like vortex generators can improve the wind turbulence problem.  The question remains which shapes work best for a travel trailer and are they really worth the cost, especially given the limited use of trailers.  For a semi-tractor/trailer on the road nearly every day at highway speeds, the savings in fuel may make it cost effective in a few months.  For a travel trailer, they may get brittle and break or fall off long before you've gotten your money's worth.  

That being said, the 172 is probably in the best shape as far as the frame and axle goes as it is a light rPod. The failures have all been in the heavier trailers in the series I believe. OTOH, 172's are one of the ones that has exhibited sway. It will most likely occur when the black and gray tanks are full as they are both behind the axle. Loading additional weight on the rear won't help that. Like I said, you can do what you want but my recommendation remains to verify your actual tongue weight percent under worst case aft loading conditions and be sure you're over the magic 10% number.