One electrolytic capacitor
And one or two of these connected to the two capacitor screws
Will really help cut down on MOTORHOME generator control panel malfunctions, refrigerator and hot water heater control failures, radios, whatever electronics in motorhome chassis. Not so much in trailers because transient spikes are generated by alternators, chassis engine starter motors and onboard generator starter motors.
I upgraded a dozen or more 24 and 32 volt fishing trawlers with these filters and just like with RVs subsequent problems almost vanished. If you want to muse something --- chew on this --- there are positive AND negative oriented transients. And OEM accessory manufacturers are concerned with one thing --- get through the warranty period. Price their electronics repair modules and see reality.