What is the best way to build a portable or permanent one?
What is a "livewell"?
. In a nutshell, it is a bait (minnows, shiners, &c) bucket with an aerator (or water pump). When called a livewell, it's usually built-in to a fishing boat. See http://en.wikipedia.org/wiki/Livewell .
Ah, Google was not my friend - brought up a load of "live well" links.L
. heehee When I saw your question, my first thought was "Huh? L knows how to use a search engine." I thought I was going to get to link you to JSFI. Then I Googled it. What a mess! I didn't try it, but "+fish" would probably narrow it down (but you didn't know it was for fishing).
. Never built one myself, but I've seen ice chests and 12V air pumps work well.