If I understand correctly, you're not starting with bare, new wood, you want to simply take your 'indoor' furniture outside and maybe leave it there.

There really are two separate but related considerations: Construction (joints and how wood movement will affect them) and wood finish.

Any wood construction will be more adversely affected by the increased expansion/contraction of the wood when placed outdoors compared to the more controlled environment indoors. Typical 'outdoor' furniture is consequently made more robust and simply in order to resist damage from that movement and/or be cheap enough to throw away when it's inevitably done in by age and/or neglect. Your rocker may get wobbly sooner outside than it would inside, but no finish is going to prevent that.

Hardest thing on a wood finish is not rain, it's the sun. Trying to paint some sort of 'outdoor' finish over a factory topcoat could be a real headache. Or not...

An opaque cover (and the discipline to use it) would be fine, IMHO. Don't lower the river- raise the bridge.