You are not grounded. I had this problem at the last house I lived in. The electric cord had 3 prongs, but when plugged in, I always got those slight "tingles" when touching the door of the trailer ... especially when barefoot.
I finally did some re-wiring in the house-garage and made sure that plug was grounded. (it was not). After that, never had the problem again.
If you don't have one, pick up one of these and check your shore power plug. You can get them at any Lowe's or Home Depot, or even on-line. They run pretty cheap.
Home Depot link, click here.![](http://www.homedepot.com/catalog/productImages/1000/05/059ad950-bce7-4669-b398-90d2ea92b077_1000.jpg)