Try some 7014, it is a contact rod that you can hold against the metal and go right along. You may have to turn the heat up some, basically the same as 6013 but contact rod.Picked up some new rod today- 7018 and 6013 3/32". Tried out the 7018 and had some fun getting the rear frame finished up. It wasn't without a comedy of errors, blowing holes, sticking rods.
Grind, Weld, Repeat.
I hit it with the wire brush grinder attachment to clean it up some and got a picture of the complete-for-now assembly:
Slow progress due to a pretty hefty learning curve, but I'm loving every minute of it
Oh, and here's my new welder!