Perhaps this goes without saying, but: top of the tank with 98 or 99 fuel with as little ethanol as possible (I think that's mostly the stuff that goes gummy) and add some stabilizer?
Other than that, yeah the trickle charger.
Someone else's probably got better tips than I do.
On the topic of the trickle charger. Likely not an issue for the Golf, but my dad once had a Buell M2 Cyclone under a trickle charger with the battery still connected and the voltage regulator actually caught fire. It was a good thing we were standing next to it when it happened. Could have burned the house down if we hadn't caught it in time. A person who actually understands electrical engineering will probably be able to tell you if that is any way a risk with the electrical systems on cars, but yeah. Could be a reason to disconnect the battery. Perhaps even remove it from the car entirely.
Good on ya for keeping the car though!