TRX-4 rear fill in and chassis crossmember for LCG battery tray

This remix combines Red Duke's 'Rear frame fill in' and the Traxxas part 'TRX8239 chassis crossmember' so that CippyO's 'Low CG Battery tray for TRX-4 easy to print' (thing ID 2848242) can accommodate a 'TRX2842X Traxxas 5000mah 7.4v 2-cell 25c Lipo Battery'.

Print
- This remix
- https://www.thingiverse.com/thing:2848242

Assembly
- fit ChippyO's Low CG Battery tray
- remove the TRX8239 'chassis crossmember' and save the screws
- remove the TRX8072 fenders or (in my case) slip aside th