If a low cost solution (aka low amperage) existed I would go ahead since the panels power area is way above where I need charge current, probably add about a 1/3 amp or so.
I fully plan on going without a charge controller and having a light switch to cut it off.
The car WILL sit for several weeks in the summer and my father fully charges it once it gets home which would mean troubles, especially with silicone gel cells.
His car sets for several hours and usually isn't fully charged during the day which makes a solar panel "Desulphator" attractive.
My main hope is to reduce battery wear which will extend cycle life, the rate of sulphation is cut well in half (or more) even under c/200 rates especially when the batteries are discharged.
I would strongly recommend anyone with an electric vehicle have a solar panel to trickle batteries, assuming they have room on the roof as it extends cycle life dramatically. Even if there is no range benefit
I have always disliked the fact that I can't fit 72v of low power panels onto my commuta's roof, I may well have to do it the hard way and split cells to build my own to run the desulphators on my commuta. Too bad a homemade panel costs more than factory made.
Many underestimate how much money is saved by extending cycle life of their batteries.
Cheers
Ryan