Choosing the correct battery is key with how you use the truck. I know a thing or two about batteries. Worked around some capable of powering a small town (10,000+ amps at 300ish volts, just a little power you understand). If you think you need a deep cycle battery, then I recommend going with a dual battery setup where you have a deep cycle for all of your loads and a starting battery for getting the motor running. I can get into the different constructions of the various types of batteries and why one is superior over another when it comes to comparing starting vs deep cycle vs marine type batteries.
Please keep in mind that in the world of batteries here in the US, you ultimately have 2 manufacturers to choose from, Exide and Johnson Controls. PERIOD!!!!!! The only difference between say an Exide battery and a Wallyworld special is the sticker on the outside and the garantee that the "manufacturer" (used loosely here) puts on their batteries. I'm sure the guys over at FTW remember the big write up I did about batteries.
So, ask away. I will explain just about anything when it comes to batteries and in a way that almost anyone can understand.
Panda, as for why at 11.6 VDC the truck starts fine, but at 11.2 VDC it won't start? It isn't so much the 0.4 VDC difference, it is the characterist of a deep cycle battery and the amount of plate left. Dipping below 11.6 VDC you start to get the plates to get thin and that results in less surface area. The less surface area, the harder a time the current has getting through the battery, leading to increased resistance. Even something as simple as 0.01 ohm increase in resistance when starting you truck (which takes about 125 amps), that 0.01 ohm becomes a 1.25 VDC drop inside the battery. Add that in addition to the 0.4 VDC difference and the possibility of the battery having more than a 0.01 ohm increase and you can really start to get serious voltage drops inside of the battery. You also have the effect of having less electrolyte, which also leads to increase resistance, but that is a bit more involved of a discussion and a good knowledge of chemistry is advantageous.