Best is in quotes, because I know there is no "best" - it is all trade offs. Anyway I would like to get some opinions from the people here.
My 27' AGP is going to get a fairly large facelift this spring.
It needs a new liner - that's a given.
The current bottom is - I assume - sand. It is quite lumpy and has a cove that varies from about 3" in one spit to over a foot in another. I say I assume it is sand because the person that owned the house before me did a lot of "interesting" things (mostly based on cost) so for all I know it could it be cat litter that he got a deal on - it would not surprise me based on other things I found done around here.
An other "interesting" thing he did is set the uprights on pieces of shale paving stone - not exactly as stable as concrete pavers. The pool is out of level by about an inch - not horrible, but not great either. One upright ice also a good inch or so out of vertical. It has not moved in the three years I have been here, but every time I look at it, it worries me.
So my plan is to pull out the old liner. Replace the shale with concrete pavers (sliding the shale out from the inside, and sliding in the pavers) and leveling the pools as I go.
I am going to go with a bead lock liner (as opposed to the overlap that is currently there) and will be using foam cove.
Where I am at a loss is what to use for the base. I go back and forth between gorilla pad and foam boards. Has anyone use either? What was your experience? I hear stories about the liner getting wedged between the seams of foam boards - any ideas besides using good duct tape to fix that? Does the Gorilla pad really create a smooth bottom? That is really my concern. I don't care so much about the "softness" of the bottom, I want it to stay flat. Right now cleaning my pool is like trying to clean a mini mountain range. What about vermiculite mix, like for an in-ground pool. Is that an option? Worth the expense?