Water leak in boot

Have a 2000 W reg Almera with loads of water in the spare wheel well, dried it out and have found, on removing panel/trim/seals that there is a rusty patch on the rear slam panel inside the boot under the(vertical) carpet trim. There are 2 bolts at this point that don't seem to attach anything to anything else. I have derusted and sealed this bit but there is still water drip dripping through this weld, even though its not raining.and it's been sealed. Have checked the boot seal/roof arial/cable trunk at top of tailgate/rear light cluster - all ok and clean/sealed and look like new (no corrosion/dirt etc). the water appears to be dripping between the inner and outer bodywork skin. Must have been happeneing for a while as there are rusty drip marks on the paint. Any suggestions would be helpful.Thanks