At risk of starting a disagreement
I would suggest you contact a local electrician and I am sure he would help you make a adaptor or rewire your location if you are permitted to do so.
Your 50 amp 250 volt and the 30 AMP 250 VOLT are compatible but will only supply 30 amps unless you can change the breaker and insure the wire is of proper gauge. Yes some refer to 110 volt and 220 volt it is all the same as there is a variable to the voltage readings. A 30amp RV plug uses ONE 110/125 volt lead and the ground lead and the ground fault lead. The 50 amp RV plug uses two opposite phase 110/125 leads and the same two ground leads. The Dryer outlet depending on the type you have may or may not have the ground fault lead.
SEE: RV Wiring
for a simple explanation. QUOTE "50 amp RV service can deliver approximately 12,500 watts (125 volts X 50 amps X 2) to the RV. Some people believe that the 50 amp RV receptacle is a "special" part. This is absolutely not true. In fact, it is a commonly available 50 amp, 250 volt receptacle. Unlike the 125 volt, 30 amp Travel Trailer receptacle, this one is used in many different 250 volt applications. It carries part number 14-50R. The matching plug is a number 14-50P.
There is a lot of misunderstanding about how MOST
50 Amp RV's are wired. Some of the larger bus type diesel pushers are all electric and in fact, do have 250 volt appliances in them. In that case, both sides of the 50 amp circuit are used to power those devices (just like your home) and those coaches MUST have 50 amp, 250V service in order to run things like the 250V stove, AC and the electric water heater. In the case of the rest of the 50 amp RV's, 250 volts is still supplied to the coach just like your home electrical service but typically one side of the line is used for all the 125 volt appliances except the rear AC and the other side is used for the rear AC only. The service coming into the RV is still 50 amp, 250 volts. Please note that all of the 50 amp RV's (at least in the US) use the SAME receptacle wired in the SAME way. If they didn't, they couldn't all plug into the same outlets at the RV park. "
Like I said consult a electrician so you do it correctly but for your lower power needs in storage it would work well.