The dual 30 to 50 adapters are generally more trouble then they are worth, They WILL NOT WORK in most parks less you have two sites.. DO not though it away though,, Because the key word is MOST.. and I know of one park that during the slow season (July/August) only allows parking on EVERY OTHER SITE and will rent you one of those boxes. just so you can use it as designed.
I also know a few other places where it works.
But they key word again is FEW places.
Use a regular dogbone with one 30 amp plug and one 50 amp outlet
If you want you can modify your RV so one of the A/Cs (rear in my case) is a plug in model (Basically you find the wire that runs up to it, and install a plug and outlet) Where I'm stuck (50 amp site) the result is OEM.. but on a 30 amp site I pull that plug and plug into the park's 20 amp.. IF such exists. using a 12 ga cord.