1. Always loot the building first then barricade.(Unless you ran out of slots).
2. Once barricaded and there are still loots and zombies, loot first than kill the zombies, or otherwise you will turn your outpost to outpost mode, which prevent you from looting.
3. When you have barricade yourself in a building, available loots and zombies will slowly disappear.
4. When there is aggro in your current area, I suggest you to find elsewhere to barricade, or you will risk dying. (Unless you are pro or have some friends to fight off the horde of zombies, you can barricade in that aggro area, if no more zombies come in).
5. If you are barricading in a 2 or more storey building, best to loot the top first then barricade. If there are still zombies, DON"T KILL THEM. First, make them follow you (make sure that it isn't a Spider, Leaper, Tendril, Brute, Bloat, Reaper or Bone. They are too dangerous to be followed. Make sure it is a normal zombie, burnt or irradiated zombie. They are the easiest to follow and safer too). Once followed, go to the loot spot in the building and loot. Make sure you hold F not E so that it's easier the use W,A,S,D to move around avoiding the attacks. Or you can use arrows. Once the loots are all looted, you are free to kill the zombies.
6. Make sure that when you are barricading, best to find a building with only ONE DOOR. That way you can save more wooden planks and nails for later. (Since they are extremely expensive when you are looting in the End Zone.

Ok, thats all the tips for barricading and interiors, comment to me by message in Dead Frontier, or here on theO (if you have an account). My username is haoliu, so any difficulties comment PLS.