Nice work so far, keep it coming.
Heres a tip that works for me about the rear wheels. I put in place the inner wheel and then using flat metal surfase (a flat screw driver for example) heated with candle, I melt the edge of the drive axle in order to make a lip that secures in place the inner wheel. After that I glue the outer wheel and I am ready to roll.
Keep in mind that we are talking about model kits, not toyz so the edge of the drive axle should be inough to make the secure lip.
Also be very carrefull playing with the fire, you have tones of plastic and glues nearby so be very very carrefull.
I suggest you to try this tip on a left over piece of sprue to have the feel of the plastic melting under the presure of the heated metal first and then try on the model.
I hope this was helpfull,
Kostas.