Any half decent battery charger will monitor the temperature of the battery and compensate for that temperature during charging. You can do this by being in close proximity and assuming that the battery and charger are fairly close to being the same temperature, or with remote temperature sensors (RTS systems).
Lead acid batteries generate hydrogen while being charged. Some dump this hydrogen out to the surrounding environment more than others. I can understand why some manufacturers would recommend keeping their devices away, especially for batteries that are in confined spaces where the flammable gas could build up. It’s a liability issue.
I’m using a Genasun GV-10 solar charge controller for my system. It is in close contact with the battery itself, fused appropriately, using very short leads. There are no mechanical switches or relays to generate a spark that could ever possibly ignite built up hydrogen. For little systems like we’re doing in the camper, this is more than sufficient. For bigger systems, you monitor the heck out of the battery banks.