The beauty of running a smart charger from the inverter strapped to your truck battery is that the trailer battery gets charged using the smart charger's profile for bulk constant amps to 14.x then absorption.
That is way, way faster than the unmodified, as is, truck charging with its 13.8v and immediate tapering to low amps.
I can easily run a 35amp Vector from the truck that way. I did it because I wanted more amps to the large battery bank and the Honda 3000 maxes out at 130amps with non-PF corrected chargers. Using the truck as a second inverter/gen, I was able to add another 35amps for a total of 165amps.
Why all the amps? A big battery bank and short allowed gen time means you need amps to get a 50-90 done in the time allowed.
