Vintage Cars: 1969 VW distrubutor cap, distributor cap, fords

Question
I have a trike with the motor from a 1969 VW (I think it is from a van).  When it rains, the motor does not want to start because there is moisture under the distributor cap.  I have been told that there is some kind of liner that can be put under the distributor cap to keep the moisture from interfering with the spark.  Does such a thing exist?  Thanks.

Answer
if you are sure that is the issue than you may need to replace the gasket around the lip. or fabricate one if it is missing.  You could also lightly spray wd40  into the cap from about 10 inches.  It would displace water and work for awhile.  They do make distrbutor covers , like an insulating jacket, I have seem them for fords , not sure about your VW set up.  there is nothing that can be put inside the cap that I know of
Sorry , but good luck
Ron