I wanted a solar trickle charger to avoid having to remove the caravan battery to trickle charge over the winter, and especially to avoid having to fit it back in which is awkward and skins my knuckles.
I did buy another kit solution but that was no good as the controller did not prevent the battery from draining out through the panel at night, and actually reducing the charge rather than increasing it. (You need a diode in the circuitry for one-way flow only.)
My caravan is an Elddis Avante and in reading other forums you have to find a 12v 'cigarette lighter' socket which is live all the time, into which you can plug the charging lead without having the electrics on continually or using the more fiddly croc clips direct to the battery. Mine is by the external 230v socket and all it needed was drilling a hole through the top of the socket box for the cable.
Charging seems steady and slow, 12.6v to 12.9v in three days but that's what you want.
NB this will NOT charge a battery which is seriously depleted, or provide off-grid charging/power.
Good so far.
UPDATE
still good, and even better now that I’ve put it in one of the roof lights rather than a front window. Plugging it into the 12 V input was problematic, now attached direct to the battery with crocodile clips and works very well. Recommended.