Actually, more useful to buy TWO adapters:
30 amp male to 50 amp female (this allows you to use 30 amp shore power)
15 amp male to 30 amp female
And, if it has a smart inverter/charger, one of the programming options is called "power share" or "power save". It allows you to limit the amps of 120 VAC used to charge the battery. If this is while in storage, no point in "slamming" the batteries with really high amps-- easier on them to charge a little slower.