Well first off I take them out of the rig, so they arent setting in the cold all winter. But I do live in northern Indiana. CTEK is a brand I used, it does have an AGM setting. Plug it in and forget them till spring.
FWIW, I have just the reg 'ol Interstate battery and remove it upon putting it into storage and then put it in cellar on a piece of wood then add just a battery tender to it for the next several months. As far as brand of tender, most of what I have are from Harbor Freight and another is Battery Minder/tender itself. No probs w/ the HF ones and I use 2 as well that I keep in the snowmobile trailer to keep 2 batts up to snuff cuz they don't get used as much as the 3rd one.
Best bet is to have a Progressive 9200 series converter/charger in your rig and leave it plugged in all the time. The Progressive 9200 series has the Charge Wizard software that runs a 14 volt desulphation charge for 15 minutes about every 24 hours. This VASTLY improves lead acid battery life.