Solar Battery maintainer during storage

Just got back from a 3 month spell in Canada - during that time our caravan has been in at a CASSOA site. But we had to leave the battery installed etc so that the Caravan/s OEM alarm and tracker were active (because removing the battery might have invalidated the insurance).

Additionally we have a TK104 Tracker connected to the battery ( https://www.caravanclub.co.uk/club-together/discussions/information-technical-tips-advice/storage/how-we-know-our-caravan-is-still-at-the-storage/ )  that sleeps in standby for 23.5 hours/day then wakes up and sends up and sends us a sms message with current long/lat. But the power consumption of this should be tiny

Prior to departure, we found that after approx 4-6weeks  the caravans standard Numax 105ah (DC31MF) battery was discharged to the level that the owners manual said would be "damaged" 11.3V (we've recharged and use it OK since)

So we needed to find a way to keep the battery installed etc but charged up throughout the typical British winter - we bought one of this 6W solar panel battery maintainer from Halfords http://www.halfords.com/workshop-tools/garage-equipment/battery-chargers-jump-starters/halfords-solar-battery-maintainer-12v-6w it comes with suckers that enabled us to install it inside the caravan on the underside of the sunroof - (i.e. no drilling holes etc) and the standard cables on the solar panel were long enough to span from the sunroof to the battery compartment.

It seems to have done a brilliant job - just checked the caravan and battery which has been untouched since beginning of January - battery was full at 12.6V - perfect - highly recommended