Here is my electrical conversion setup:
I have 2 Interstate MT7 AMG deep cycle batteries under the hood. These have better performance under adverse conditions (cold being my primary concern), still provide adequate cranking amps when the battery is low, and are meant to be discharged/charged without hurting the battery life (note: normal car batteries are not designed to be discharged all the way and then recharged, their lead will not properly re-plate upon recharging.) If you want to keep it simple, just put one of these in your truck, they are much better than normal car batteries.
My alternator runs through a Stinger battery isolator and relay, which distributes charge to the 2 batteries and isolates them during discharge, so I can completely discharge my secondary battery without worrying about cranking. Or, I can completely discharge my main battery and jump my truck from the secondary (this should happen automatically, but I have cables if it doesn't.) I was somewhat concerned that the stock alternator wouldn't be able to handle this setup, but an expert automotive electrician told me otherwise, and I haven't had any problems over the last ~8 months.
My secondary battery is currently wired to 2 places - the inverter under my back seat, and to the LED light setup I have in the bed. When the inverter is on, it provides power to an outdoor rated ac power receptacle in the bed. There are 2 open outlets to power electronics inside my truck (phones, laptops, & other equipment that I need when working in the field).
(~ bed is currently a mess, and I'm in the process of rewiring the LED switches because the wire won't stay tucked under the bed rail during off-road driving)
Overall, I've been very satisfied. I've camped in the bed in relative comfort during adverse conditions (-20 F + blizzard was the worst night I believe). All of the air gaps under my bed rail are sealed to prevent drafts and I have an inflatable "donut" that seals my trucks back window to the topper. It still gets cold in the topper on those nights, but a 3 inch mattress topper, -20 F sleeping bag, and a heat blanket are plenty to stay comfortable. In the morning, I just fire up the truck (remote start) ~10 minutes before I get out of the sleeping bag, and I keep a Mr. Heater Tough Buddy handy if that isn't enough.