"I am wondering what the groups opinions are about the best end fed antenna
lengths would be for taking my newly built KX1 mobile? "
For 40, 30, and 20 meters, I use a 42-foot wire with a large nut on the end. The wire is thrown over a tree branch. A Pomona BNC-to-Bindng Posts adaptor is used. Three counterpoise wires cut to one quarter wave for each band (approx. 33', 23', and 16.5') are connected to the ground binding post.
I have worked EU DX from my dining room table with the antenna wire going over the top of the back door out to a tree limb and the counterpoise wires spread out in the other direction on the floor.