Many car holders are available in accessories:

https://lapmonitor.com/store/en/13-accessories

Some transponder mount are available for printing

https://www.thingiverse.com/LapMonitor/designs

Traxxas

Slash

Please check this video:

https://www.youtube.com/watch?v=wfo4-UcSRcY

Rustler

Transponder model used is ref: TP_JST_01

Buggy 1:10th

B6.1 Transponder holder

XB2 Transponder holder

Other 2WD examples

XB4 B74 YZ4 Transponder holder

Buggy 1:8TH Brushless

Team Associated RC8B3e

Mugen MXB7/8

Free 3D model: https://www.thingiverse.com/thing:3005753

Carbon version

Tekno EB48 2.0

XRAY XB8e

Free 3D model: https://www.thingiverse.com/thing:4300695

Carbon version

https://lapmonitor.com/store/en/accessories/55-transponder-mount-for-xray-xb8e-tlr-8ight-xe-hobao-carbon.html

TLR-XE

Buggy 1:8TH nitro

Generic solution

KYOSHO MP9/10

XB8