Isolate all of your electrical consumers using a masterswitch. Charge your leisure battery and starter battery - use recond mode if it’s lead acid but not if it’s AGM - and disconnect once charged. Top up starter battery periodically in case of drain.
Drain fresh water, waster water, toilet flush and toilet cassette (if you have it). Purge taps and flush by running the pump (taps open) with no water in the tank. Wipe down all hard surfaces with antibacterial spray, and give the fridge and freezer a very thorough clean, leaving the doors ajar.
Take your bedding indoors if you can. Leave all interior doors and drawers ajar for circulation. Make sure all windows and vents are closed. Close the blinds. Lock the door. Plan where you’re off to next year. Sorted.
PS I wouldn’t leave it on trickle without regularly checking it, especially leisure batteries. If a cell fails then the heat and pressure can build up and the resulting acid leaks or high pressure evacuation is a bit of a nightmare.