The current wheels on our bike trailer are cheap and use a one sided hub design that uses a small ball bearing to hold the wheel on, you have to push the other side for it to release. I guess this is to aid folding and packing away.
My idea for having a sturdier set of wheels is new 20 inch front wheels and using a length of threaded bar (5mm normal quick release?) create a long axle using bolts, it would be around 70cm long. Would this work? The wheels would be joined together and in my head a better setup than using a small ball bearing to hold the wheels on
Threaded bar is very soft and weak generally. I really do not think it would work for axles.
What's up with the wheels?
What tj said too
If the wheels are joined together it will make cornering harder. Is it wheels themselves or the stub axle you want to replace with something more robust, or both? I don't follow how you plan to attach the axle in terms of bearings.
if the system on your trailer wheels is one of using a ball bearing on a spring as a retainer then this is a very robust system used in wheelchair wheels, walking sticks, crutches etc and one I have never seen fail