Talk with your AHJ for what they may consider acceptable since this would not be an RV park in my opinion. Some things would not likely change such as the need for disconnecting means which is why I like the prebuilt units. That said, they do offer, or at least in the past, weatherproof covers for this size of receptacle. The weatherproof cover I have on my trailers connection at my house is a Taymac.
Loading is the big area to discuss with the AHJ. Likely you will need to tap off a feeder which requires overcurrent protection for the receptacles, another reason for the prebuilt units. Otherwise if the loading and if manually controlled cylcing of AC's (which I doubt will happen)could mean that a 30 amp feeder may provide power for all 30 amp receptacles, and a 50 amp feeder for the 50 amp receptacles. I would not approve this myself because rather than manually cycle the AC, the AC will be left on (likely a high setting) as soon as I leave and over load a shared small feeder.
Lastly depending on the code cycle and code interpretation, be prepared to install grounding electrode (ground rod) at each disconnect due to the 2008 NEC 250.32 and the diffinition of a structure in 2008 NEC 100 "That which is built or constructed."
Though this does not pertain to you, I am inclduing this for information for others. As this is storage it is not a good idea to plug in and leave a trailer connected up full time for extended periods as batteries will overcharge and be ruined. Yet to leave a trailer disconnected from any power source will discharge the batteries and leave you in the same bad spot (it is amazing how fast just a propane detector can drain batteries). I recommend removing the batteries during storage and an occasional trickle charge. A battery disconnect installed on trailers with gel (starved) cell batteries which can be switched on for 1 day a month would also work, but is not a good idea for wet cell batteries.
