The above postcode is for The Waterside Centre, Dreadnought Reach, Reading
You could retrace your route to the A4 and follow the A4 right into Reading.
Or, you could take the A4 westwards in order to get on to the M4 at Jct 12.
Take the M4 eastwards towards London
Exit M4 at Jct 10 (it feels a very long way but it avoids going through the centre of Reading on Easter Saturday)
Leaving M4 at Jct 10, turn towards Reading (M329).
Follow this road to the very end (it becomes A3290), ignore all slip roads and signposts. Eventually you run out of road and arrive at a roundabout, where you have to turn right (there is only one exit).
As soon as you turn right, drive slowly - 20 yds up the road you will find the entrance to a car park on your left. You have arrived.
PARKING - if you are lucky you might find a space in the car park. If not, you will be able to park alongside the road - everyone does this. Then just walk back to the Marsport Waterside Centre Building.
FOOD - stall selling tea, coffee and chocolate bars. Lots of places to sit to have picnic.
LOOS - in the Waterside Centre building, up metal stairs on side of building
NB If you want to see the boats coming along the K&A canal and joining the River Thames you will have to walk about half a mile southwestwards.
This is a compulsory portage so although there is no lock all the crews have to get out here. You will therefore have a chance to get quite a bit of food and liquid into them as they can put their boats down for a short break of a few minutes.
Map - Click SAT for aerial view
There is no supporter access to Sonning Lock or Shiplake Lock so your crew has a long stretch without support between Dreadnought and Marsh Lock.
The next vantage point is Marsh Lock