Dick,
The product is Dicor Lap Sealant. It is available at your local RV Dealer.
Here is a description from Dicor's website:
EPDM Rubber Roofing Lap Sealant
Dicor Lap Sealant helps create a watertight seal along a roof's edges, around air vents, vent pipes, air conditioners and screw heads. Compatible with EPDM rubber roofing, it offers excellent adhesion to aluminum, vinyl and galvanized metal. It improves the ability to continuously seal and remain flexible. The lap sealant is UV stabilized to prevent deterioration and discoloration and will not stain or discolor any material to which it is applied. Available in white, ivory and dove gray.
Here's a link:
http://www.dicor.com
Look under the care and maintenenace tab.