I've run into this issue many times on all of the 4 x 4 forums I am on for trucks.
I've written a few "how to" threads on it, and in my opinion, without stepping on anyone's toes, the industry has made this far more complicated than it needs to be
Batteries of the same exact type, isolators, blah blah blah, you've heard it and read it 1 million times.
Every single truck I have owned I have done a dual battery set up and I've done it for 150 bucks.
If you want to do an in cab set up, expect on getting some longer lengths of battery cable which can run you around 250. That's for a regular truck now. For a UTV it will be a cakewalk.
Because my last truck was a diesel Duramax it already has dual batteries so it's the only one I didn't have to do it on.
Go down to any marine store and buy a dual battery switch. Or Amazon. $25-$50
It has battery one, battery two, both, or off. Install your second battery and wire accordingly which is very very easy. One battery goes to the in, other battery goes to the in and there's one output.
Put the switch under the hood and alternate batteries every couple weeks to keep them charged and ready to go.
When you need extra juice like winching or something, put the switch in both and get the power of two batteries.
If you really want to go fancy, put the switch inside your truck and cut out a hole and mount it on your dash to look really cool!
That's it all done. Buy the switch, by the battery, buy some terminals and battery cable and I have yet to have one of those systems ever fail and they are bulletproof!!