Getting consistent colour scans has always been a nightmare. The automatic options in VueScan or Epson Scan end up giving each photo on a roll a slightly different look which in turn means lots of manual correction.
I decided to do some googling and came across two good tutorials which both work on the same principle. (Tutorial, Tutorial) You scan the negatives as if they were slide film so you capture the orange mask, you then cancel that out in photoshop, then invert the image and balance/contrast the colour channels. Its a bit fiddly to start with but seems to produce consistent results and gives you a great base for further tweaking.
I shot a roll of Portra 400 when I was down in Eastbourne the other week and just got the negatives back from the shop. Below are a couple of examples, including an accidental double exposure (I don't have an obsession with those life rings honest). It was an overcast day with no direct sunlight so don't think the colours are a million miles off.