For economy you can stick w/standard AntiFreeze formulated for diesel trucks. It comes in premixed (50/50) and 100% and includes the necessary additives right from the jug.
If you check the additive level w/test strips available from any NAPA or other truck part store about every 6 months (they can also sell you the additive), you should be able to run the same coolant for double or so the 2 year time frame.
If you don't test, replace at 2 years for sure.
You can check out "permanent" antifreeze types online. Google "oat antifreeze" or "permanent" AF and read up on whether that would be a useful option for you. I had DexCool in my last rig, and it was kinda nice not to have to mess w/it. That rig had a cheap aluminum radiator (GM, nuff said) and I never had the troubles a lot of other folks w/the same rig did with their cooling. It is spendy, and reportedly finicky about purging the air IIRC.
Some say their antifreeze can be mixed w/any other. I'd steer clear of that, and do a completer purge & install new of the same type, or purge, full rinse w/distilled water, then install a new type. Whatever goes in, I'd carry a coupla gallons spare 50/50 mix, just to insure you never ever have to mess w/it on the road.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project