At 3c disconnected I seriously doubt those batteries would lose 10-amp hours total in 5-months. Unattended being disconnected means those batteries will be immune to anything and everything. 100% lrotected. The odds run heavy to disconnect, switch off the converter and solar and put things in full hibernation. AGM batteries love cold weather hibernation. Pull a ground cable if you don't have a full disconnect switch.
Your particular scenario favors disconnect versus unsupervised float charging so heavily it's not even a fair contest.
