I think that is the tricky part done. We bored the long box section for the axle (a length of 19mm rod), the hub ends are capped with a piece of plate also bored to accept the axle. The wheels have bearings, so I have a thrust washer and a snap ring pin to hold them in place. I thought about welding the axle in place but I don’t think it needs it.
I’m just using a mig welder. It might not be the best tool to use outdoors, but it stops welding and grinding sparks hitting the ‘ tool shelf’.
The wheels are parallel, my phone camera lens gives them positive camber.
The trolley the materials are on is from a station platform. It weighs a ton and has solid tyres. It’s near impossible to pull even unladen on rough ground.