A portable setup is better off with only 1 battery.
Here is a no thrills controler idea for qrp up to 100 Watt power levells. The motor is reversed if the zener diode recieves more than 9v from the 3 position swich. At 6v the relay is not activated so the motor runs forward. The chokes and diodes should be able to pass at least 1Amp. Chokes have 16 turns 0.8 mm transformer wire on a FT50-43 toroid. This controller is designed for 360 degree tuning capacitors . 180 degree tuning capacitors need protection by means of 2 miro switches and reversing diodes between the relay and the moter.
By adding high voltage capacitors ( silver mica ) for C1 and C5 this cotroller will handle 100 Watts.
The relay is activated by means of an over voltage protection circuit . To avoid RFI a small metal box is used for both units.