I would do 50. This effectively gives you two legs, each 50 amps, so really, 100 amps, or 12 kilowatts, while 30 amps only gives you 3.6 kw.
As for power inlets, I am wondering if going with Marinco cords and receptacles might be an idea. The reason for this is that their products have a secondary twist lock and an outer ring that helps further keep water and the elements out of the outlet. If this is a tiny house that may stay in a location for a time, might as well do the job right.
Oh, don't forget SWD rated breakers. Since you should be flipping power off at the breaker when connecting and disconnecting power, it is a must to have a switch rated circuit breaker.