On a 2619 like mine (with Batteries on the Hitch Tongue, behind the Propane Tanks) the installation would be inside - because, at roughly $1000 each, I would not want those batteries exposed to thieves. (They don't emit hydrogen gas, and are safe to use inside - without venting.)
Good Solar controllers are easily re-programmed to provide "correct" voltages to batteries which have built-in BMS. (In particular, the "Float Voltage" needs to be brought way down - about 13.2V.) But older TM power converters and cheap replacements (WFCO, Boondocker, Parallax) are not programmable, and the too-high "Float Voltage" presets (~13.7, maybe even 13.8V) will cook the LiFePO4 batteries in fairly short order. So the shopping list probably needs to include a new Converter, and not just new batteries.
It is sometimes said that you can discharge these batteries "all the way to zero, without damage", but I think that's not actually true. Going below 10% SOC on a regular basis does hurt them, so a Battery Monitor (programmed for LiFePO4 SOC characteristics) would be a good thing. Still, If you buy "200Ah" of 12v Lithium batteries, you can comfortably use up to 160Ah of that capacity. With SLA "safe" battery usage limited to about 50%, you'd need 320W of labeled capacity to match 200A of lithiums - and they'd weigh a lot more. And they'd all become worn out in 4-5 years, rather than 10-12.
There's are two place in my town which assembles and sells these batteries for RV and Marine use (12V, with BMS already built-in), along with the relevant add-ons and upgrades you probably need. Give 'em a look, and read their FAQ:
https://battlebornbatteries.com/, is one good place (selling their own made-in-USA batteries), and
https://theinverterstore.com/ is another. "The Inverter Store" is the retail web outlet for AIMS, which sells imports from China under their own brand.