I threw this together 2 weeks ago when it was time to go to the airport, and I needed something quick. A friend has lots of alum., so I took what I thought I needed, and it worked. The round tubes that go around the axle bolt are steel. The rest is thin-wall alum. I think it is 1 1/4" square, very thin-wall and light. Pulled the heck out of it to get the fuse up the ramp into the car hauler, so it seems strong enough. Simple bolt for a latch. Rivets for a pivot. Might weld some areas later.
The model 4-RVA fits the RV-12 nose gear. It clamps to the wheel bolt which seems fairly secure, but you can add the tow pin kit which increases the engagement.
And, you may want to pick up a jack pad (plan ahead), the Bogert ADJ-FPP fits the RV-12 main gear leg nicely.