Two thirty amp circuits give you a lot of power and flexibility. Use a 50 amp Marinco splitter to split the 50 amp service
into two 30 amp.
You will need to install a new shorepower inlet, hopefully right beside the existing one. Then add a 3 breaker panel somewhere next to your existing one. Use a 30 amp breaker as the main one and then wire that one to the second and third. Wire the shore power
inlet to the new panel with 10 guage wire.
Now install a 15 or 20 amp breaker in the 2,3 position and wire it to a dedicated convenience outlet for your second electric heater
Oh and if you want to meet ABYC standard, then install another 30 amp breaker near the new inlet.