Big Ask that, give these (the routes go from south to North so invert them if you do them)a look and then pick the bones out of them these will cover the Welsh side. For the Ingrish side try M4 to the Bath junction--A46-A420-A350/1 then pick up the coast road to Ringwood or there are loads of options like A4 too Marlborough A346? to Andover and then from winchester pick up the B road just off the M3 after the downs to Fisherspond/BishopsWaltham/Wickham
not got mapsource then sorry someone else may have input