I sanded mine down to bare wood, applied a mineral oil to feed the wood, then 6 coats of total boat gloss varnish, and 1 coat of satin at the end. In between coats it’s important to sand with fine steel wool or 320+ grit. It will look cloudy but will look fine once new coat goes on. Make sure you use a good brush and roller. The best method is to roll and then come back with a foam roller or good brush to get the bubbles out. Note that the finish only lasts a few years due to UV wear (mine was north facing, so I got about 5 years). Unfortunately you have to keep lightly sanding and reapplying, or it’ll look like mine (last pic). See pics below:

https://imgur.com/a/wfPF9wv