The adapter you are showing is a 30 AMP and 15 AMP that allows you to plug a 50 AMP cord into the adapter and get 45 AMPS
Right - I was suggesting that it might be better to convert the camper over to a 50 amp plug and it might make your life much easier in the long run - but I realize that is quite a bit more work.
The potential problem I see is that you could end up pulling both plugs from the same leg. You run the risk of overloading one leg if the pedestal can not support that much current.
This may be a better solution given your wiring situation:
This should pull 30 amps from each
leg and you dont run the risk of overloading anything. Only downside is you can only run one AC unit if you are at a 30 amp only site - but I think you would have that limitation anyway.