Insulation installation questions

My questions are probably pretty basic but I've never done any insulating so I know nothing about it.
I looked at the foam board type insulation at Home Depot. All they had was 1/2". Is that enough? Seems awful thin to me.
Moisture barrier? Is that something separate from the insulation? What is it? What does it look like?
Do I just jam the insulation between the square tubing in the walls then cover back up with the boards that are now on the walls or is the insulation supposed to be fixed in place some way?
Is the insulation supposed to touch the outer skin of the trailer or is there supposed to be a gap between the skin and insulation?
Any pointers would be greatly appreciated.
Here's where I'm at now... Just starting. I do have a portable A/C inside so I can stand to work inside in this Louisiana summer time heat.

I looked at the foam board type insulation at Home Depot. All they had was 1/2". Is that enough? Seems awful thin to me.
Moisture barrier? Is that something separate from the insulation? What is it? What does it look like?
Do I just jam the insulation between the square tubing in the walls then cover back up with the boards that are now on the walls or is the insulation supposed to be fixed in place some way?
Is the insulation supposed to touch the outer skin of the trailer or is there supposed to be a gap between the skin and insulation?
Any pointers would be greatly appreciated.
Here's where I'm at now... Just starting. I do have a portable A/C inside so I can stand to work inside in this Louisiana summer time heat.




