just curious, i know you will be using a liner but have you considered sealing or treating the frame since it doesn't appear to be pressure treated?
I figured at the very least a little BLO or deck seal for the wood or something like spar varnish. more expensive would be resin/fiberglass.
it would be a shame if the liner sprung a leak and the water destroyed your finely crafted wooden structure. or worse, it sprung a very small undetected leak and over time the structure weakened and then gave way one day.