depending on the battery chemistry yeah sometimes, I get a good 20A out of my fixed panel while driving and that seems fine for me.. I dont really need charge while driving but it is super nice to cook while driving, figured out how to secure a crockpot for road travel.. with LFP and no fixed panels on roof I think I'd invest in more power from the tow vehicle, just to get the most out of my engine runtimes.
my last trailer with lead batteries it ended up being pointless expense and effort, I upgraded all the wiring to the trailer but then only did a few days of 6-7h travel on a 2-3 week vacation, most days were moving camp a few hours down the trail/road.. didnt even bulk much.. ended up having to find shore power every few days when solar conditions were not cooperating cuz I didnt have a genset.. now if the house bank was in the tow vehicle its a whole new ball game, just puttering around sight-seeing is filling the bank when a trailer would be back at camp, likely shaded cuz your not there to move the panel over a few feet.