I have a 50AMP TT, but I wanted to be able to incorporate the 20 GFCI receptacle at state parks (without tripping the GFI) or use both the 50 and 30 amp connections and this is the only SAFE way I found. I wanted to run both AC's and a microwave and not worry if the ice machine kicked on too. Some homemade brews could be a disaster waiting to happen if the park is wired with multiple phases feeding the plugs. To me, it was well worth the money and time to install this setup. I get 50 amps of service on a 30 amp site or 70 amps on a 50 amp site without straining any components! The JTB automatically "removes" the main A/C from my main panel when the JTB is plugged in so it doesn't count towards my main panel amperage draw. When the JTB is not plugged in, the main A/C is still part of the main panel. It's a "smart" set of automatic relays that won't trip the GFI.
Here's is my JTB Power Solution System installed in my Denali 266RL 34' TT. I also have a Progressive Industries EMS on both the 50AMP Main Panel service and the 30AMP (Technically 20AMP) JTB service. I did not opt for the install kit as I intended to use a 30 amp twist lock power inlet to match my 50 amp main inlet. Also I was running short #10 wires, so the install kit is not pictured. I also purchased the yellow 30to20 amp adapter by Marinco (#126A), but it has not arrived yet, so is not pictured.
I also chose to add a receptacle to my JTB box which can be used only if the main A/C is turned off at the thermostat. I chose to "JTB" my main A/C rather than my second A/C because that is the ducted unit that we will always be using. It also is the larger unit and pulls more amps, so I isolated it to the JTB which frees up more available amps on the main 50 amp panel for the microwave, uline ice maker, hair dryer, and other appliances. If I did the bedroom AC on the JTB then I am limiting the amount of time that I actually benefit from the JTB. Haven't been camping as I just finished the install today, but connected to power at home and everything works as expected.
Here's the slideshow photos: