Which trickle charge solar panels for our caravan?

There is already an extensive recent thread on this subject in the "Storage" section, did you not find the answer there?

All will depend on the caravan's parasitic drain on the battery, and the battery's own self-drain, but a 1.5 Watt solar panel facing the challenges winter will present is way-way off being confidence inspiring IMO.

Winter has short light hours, low sun angles, typically is more overcast then there are the potential issues with dirt, leaves etc getting stuck on the panel. The low sun angles mean much greater issues with shadows, poor yield if the panel is mounted horizontally though if not the sun tracking round means a short optimum alignment.

IMO to have a decent chance of coping with solar through the winter then the panel size has to be what on the face of it would appear grossly over-sized. I suggest at least a 40 Watt panel well placed is needed to have a reasonable chance of not failing; then an unfortunately blown wet leaf could let you down.

does the battery need to support an alarm or tracker?

if not, just take the battey out, bring it home and give it a charge periodically.

I have been using something very similar to this one " Solar Panel " for about 4 years now on my motorcycle. It sit's idle for months on end sometimes and has an alarm/immobilizer that puts a small draw on the battery.  I was very sceptical of it for the money but it does the job and is cheap  

Given that even a large motorbike battery is only about one tenth of a leisure battery, I think a larger panel would be needed.

I agree that the battery is of a much less Ah rating, below 20 in most cases, (14 for my Triumph) but all your looking for it to do is maintain the battery in the condition you left it. 

These type of devices are not intended to charge a battery, just maintain a level of charge whilst the battery is not in use.  Alarms draw mA's so are not really an issue either. If want to recharge a dis charged battery then you need to start looking for higher Wattage form a much more expensive solar panel.

Can't help but echo Ocsids words. At least a 40w panel due to the conditions of our winters.

Had the same challenge and I am very please with the solution which worked for me.

It will depend on your circumstances - but I need to have the OEM alarm enabled plus I have a separate GSM/GPS tracker which is in "deep-sleep"/standby for 23.75hours/day.

My Caravan battery is also 105amp hr.

I initially installed a 2.4w solar maintainer sold by Halfords, during the dull short daylight days of winter is wasn't up to the job.

I then upgraded to the 6W solar maintainer which I bought from Halfords (but is also a few £ cheaper from Aldi) - it proved powerful enough throughout the winter - and in our case it is slightly smaller than the main sun roof so it was installed inside the caravan so there were zero issues of creating waterproof roof penetrations.

It was discussed more here https://www.caravanclub.co.uk/club-together/discussions/information-technical-tips-advice/storage/solar-battery-maintainer-during-storage/

40W recommended above is IMO more powerful and expensive than really necessary