Fix it now or wait?

The only difference between today and tomorrow is how much of that quarter will be replaced.
If I needed to wait for the time and money to fix and paint the whole car I would first remove the plugs in the turn downs underneath and flush that area well from inside the trunk, then flood treat it with a rust reformer product. I've used the water based Rust Ender with satisfactory results.
That along with a new trunk lid seal didn't cure the cancer but did slow it waaaaay down.