I use a 'jr.' on my 2 x 6V batts that I use for my trailer. They're a 3-stage, AFAIK (the very best will be 4-stage (desulfation mode)) That said, 3-stage is fine for the Jr., for what I use it for, and prolly fine for you, too.
Just keep in mind that the jr charges at a lower rate (my 6v model is something like 500 milliamp, iirc). If your battery is low, you may be waiting 2-5 days for the light to go solid green (maintenance mode / trickle). But it'll get there...eventually. And when I checked the water level the other day after about a month, it was fine (which, at that low load, I'd expect, frankly!)
The 'Genius' chargers look promising (nice featureset), but they're spendy - and geared more toward quicker charging / starting.
I have a 4-stage Schumacher for my 12v. It'll act as a maintainer, and can handle my deep-cycle trailer batts, but it's a dedicated 12v. It also is acting goofy (mostly display, but I can't trust it to leave alone, long-term), and since it's an occasional use charger, I can't recommend them any longer. That's why I got the 6v Junior, instead of hooking up the trailer batts in series and letting the Schumacher handle them.
Now - with all of that said... if you fully charge the battery, and simply disconnect it, as Moose said - that might work for you. But - I'd put a charger back on it for an hour or so before using it to start the truck again, so as not to potentially tax the alternator.