I tried cutting back the weaving a bit and slowed down; penetration did improve (as viewed from the back). Here's 1/4", preheated to ~400F, Miller 135 running .030 wire
Also, kind of hard to see in this pic but I added a 1" long piece of heavy wall tube to give clearance for a nut & washer at that part where my weld got too close to the hole.
And this concludes all the heavy frame fab work - thanks for all the help everyone!
Here's the motor sitting in the frame: