I have always been of ther belief that vapour lock was when the fuel in the fuel pump boiled, causing only gas to pass into the carb.
One possible fix is to use the fuel filter that was used on Valiant 6's This was placed AFTER the pump & had a small, metered secondary outlet on the top face. This allowed some fuel to pass through the pump at all times & helped to keep the pump "fuel cooled" The fuel that was bled off was returned to the tank. It also allowed any vapour from a heat soaked pump to jet straight back to the tank.

If you give it a try, use it in conjunction with any other method that may be advised, including the use of a Bluebird electric pump at the rear.
I run a triple row radiator in my 200B & even with the AC on, no problems.
Chris