A lot of good advice here. I would first agree that in central Texas you don't need something as expensive as RimGuard. If you don't get hard freezes more than occasionally or overnight then plain water should be fine. I plan on using windshield washer fluid (ie methanol/water mix) but I'm in a freeze zone.
The advice on filling tires yourself with adapters from TSC is right on but I didn't see anyone mention that you need to be careful to jack up the tire a little first and block the axle before you remove the valve mechanism. You don't want the tire unsupported. Most authorities (ie tire manufacturers) recommend not filling more than about 75% so you still have some air to allow the tire to be flexible. Best way to measure is simply to put the valve at about three quarters from the bottom (probably not right at the top unless you are going to carefully measure the fluid you put in).
I'd be REAL careful if you are thinking of removing the tire to fill it (no particular advantage for doing that other than taking the tire to the dealer). Remember these tires/wheels are heavy to begin with and that adding even plain water adds over 8 pounds per gallon. My DK40se rear tires will gain about 400lbs each when loaded with WWF and will end up weighing over 600lbs each. That is a potentially very dangerous thing to be manhandling.