Er well after much scraping of underseal and general messy gunge-removal from the wheel arch in question the measure of the job seems to be becoming clear. Whilst it's a bit more than bargained for (as ever) it should be managable - as one job it's hideous but as several smaller jobs it should be ok.
My panelbeating hammers turned up a while ago and I went and harrassed my local steel supplier for some 20swg sheet and set to work...old sessions posters make great templates for marking out shapes of panels :D
Since ther's a number of small plates which need to be created and then welded in and I've never done anythgin like this before I figured start with the least structural/complex bit - namely the raggedy rusting bottom bit of the inner-inner wheel arch (sos don't know the correct names for the panels lol).

Ragged as f**k
Well basically it all works just like in the book - clean up the area, mark the bits to be made, cuyt shapes out of metal, hammer to shape and fit...
well I've still got the first fitting to do but shaping the metal (inc folded edges and swages) etc was actaully the easiest bit! Go figure..

New section formed from sheet with hammer & dollies (not doilies)
Strangely enough - having all been measured by eye and with a bit of card, it all seems to fit perfectly. Note the matching swage/curvy bits where the new section meets the beam, rolled edge and lapped edges for strong join to the original panel...
we is getting there =D