I've been wrestling with this exact problem for the past couple of years. During summer when I'm away from the shepherd's hut for weeks on end, the battery bank just sits there fully charged with nowhere to go. It's actually quite inefficient from a longevity perspective.
What I've settled on is dropping the charge controller setpoint significantly — I run mine at around 13.2V absorption voltage instead of the usual 14.4V. This keeps the Lithium cells in a much happier state of charge (80-90% rather than maxed out) and reduces stress on the BMS during those long idle periods. Obviously this means less usable capacity, but it's a fair trade when the house isn't occupied.
The other consideration is load disconnection. My Victron MultiPlus sits in passthrough mode with a tiny trickle draw — probably 20W at most — just to keep the system alive. I've removed any unnecessary always-on loads. Some people advocate actually isolating the main breaker entirely and just monitoring voltage remotely, though I'm not keen on that with lithium as you lose BMS oversight.
Battery temperature is worth monitoring too. A warm summer in a closed-up hut can degrade cells faster than you'd think, particularly if charge voltage is too aggressive.
Has anyone else found a better approach? Particularly curious whether anyone's using load control systems or seasonal profile adjustments on their charge controllers — I imagine the newer Victron units might have some clever firmware options I'm not exploiting.