Some of the new Lithium batteries are “self-heating”, so that should take care of the first concern. That is assuming that you have some way to charge during storage. As far as negating the benefits of Lithium, that depends on what is important to you. To me the benefits are: 1) higher operating voltage and very little voltage droop under load, 2) more capacity per weight and volume. The downside is cost, but the prices have come down considerably over the last couple years.
As far as needing a new charger, it depends. If you have a charger with programmable parameters, chances are you can set it up to do a good job charging Lithium. From what I’ve seen, charging Lithium is more simple than charging lead acid. Pretty much constant voltage, no float and definitely no equalization. I have a Bogart charge controller and have found settings to use for Lithium. My on board converter (for shore power) is not programmable as far as I know so I will most likely have to change that. (I have 2 100 amp-hour lithium batteries, but haven’t installed them yet).
I would guess Lithium batteries are about 1/2 the weight of a comparable lead acid battery. But you get more usable amp-hours from Lithium, so the effective weight saving is even more.
I’ll be interested to see what others have to say.