If I need to boil something for a long time (pasteles for one hour or tripe for 4) and I want it to happen in my absence, can I do it in the oven? What would be the right temperature to set the oven (don’t say 212oF, it won’t boil)? Any warnings, tips, caveats or others I should be aware of? How does energy consumption compare (gas if it matters)?
A slow cooker might be a good option. Mine will maintain stuff at a low simmer. Personally I would feel safer about doing that in absentia than leaving a gas oven on.
My gas oven does a lot of my cooking while I am not there watching it. This is how we have a hot meal when we get home after I run the gauntlet of picking up everyone from school/work, etc. That is really not a concern at all. I would just like to widen my uses of such technique to include things that are normally boiled.
I, too, cook in the oven when I’m not there. Mine has a timer which switches on during the day, so that in the morning I can put into it a frozen pot roast or cut-up oiled vegies and have them start roasting later so that they’re ready for dinner.
I don’t see why you can’t fill your dutch oven with liquid, pop in a chicken or vegies or whatever, and let it simmer in there. If you had browned it first and used minimal liquid, I suppose you’d technically be braising it, but I won’t split hairs over definitions. In fact, a chicken poached this way would probably be scrumptious.
I use a coffee maker for this kind of thing (old college trick since we couldn’t have stoves/flame in the dorms).
It’s good for pastas/rice/beans whatever, and since the pot has a strainer I already just cook it, drain it, dump in sauce and eat from the pot.
Yes, I’m single. Single and efficient! 
I wouldn’t be surprised if there are some recipes where reaching a boil is in fact a necessity. However, for nearly everything I am fairly certain that “boiling” is simply a visual cue of the temperature you are at. Specifically, that you’re a temperature sufficient to cook with.
You might actually prefer to cook at sub-boiling temp in the oven, just so you aren’t producing as much steam. But so long as the oven temp is high enough to cook, once the water in the pot reaches that temp, it doesn’t matter whether it is or isn’t actually boiling.
Let’s say, for example, that I have some pasteles (think tamales) that need to be boiled for an hour. What do I need to do to have that happen in my oven?.
I haven’t done that but I have braised stew in the oven. If they are completely submerged, then it’s nearly impossible to set the oven on too high a temperature since the water won’t ever exceed boiling (whatever temperature that is at your elevation). So I would bring the pot to a boil on the stove (to get off to a quick start, but not required) then put it in the oven at at least 250, but not more than 325. The only danger (which would be as true on the stovetop) is allowing too much water to boil off.
As far as energy efficiency, it depends on how well insulated your oven is. On the stove, the heat is directed narrowly at the pot, but the heat loss into the cool room will be fairly rapid. In an oven, the question is how fast the oven loses heat to the room. (True, you have to heat the entire oven to heat the pot, but that’s just the startup phase and not too much compared to the rate that heat that is lost to the room once it comes to equilibrium.)