I would recommend this place for parts as I don't do CW. As previously stated, do it right the first time instead of the half-.ss approach and it will work every time.:C
http://www.rvupgradestore.com/Portable-Surge-Guard-50-amp-p/55-2569.htm Great service, quick shipping, no hassle returns if there's a problem.
You will also need to have a dogbone adapter on hand for those few times that 30a only service might be available for your 50a rig.
http://www.rvupgradestore.com/Power-Grip-Dogbone-50-amp-female-to-30-amp-male-p/55-8403.htm