You may want to modify things a bit.
I would want to run 10/4 (3 plus ground) since you should not ground sub panels save back to the main, Even though most parks do ground the sub panel. I do believe strongly in safety grounds.
and Id like to run separate legs to the 30 and 20 amp outlets. (though this is not needed if you upgrade the underground wire to 50 amps)
Best option.. Get a 50/30/20 amp box and either feed it with 50 amp capable wiring and breakers or use 30 amp breakers back at the house, then put a bit of Gorilla Tape over the 50 amp outlet and/or disconnect it at the breakers .
Advantage.. If you ever upgrade to a 50 amp rig...Zero cost upgrade of panel.