These battery powered security alarms would suit you. I had one similar to this in an outdoor shed a while back. It comes with a remote control to turn it on/off. They make a lot of noise when activated and would scare a would be thief off. You could easily set it up somewhere in the tent or on the tailgate of your CT. Set it with the remote as you leave and it will watch your property.
Specifications Are:
Bright LED light or siren is activated when there is movement detected by the PIR sensor
Powerful, loud 110dB+ siren sounds & light turns on when there is motion
Switch between 3 modes on side of sensor: 'Alarm' (Alarm & Light), 'Light' (for Light only) or 'Off'
Includes bracket for easy wall mounting & remote control with 100ft / 30m range to activate & deactivate the alarm & light
Use as a motion triggered light while you're home or a motion light & alarm when you're away
Main unit requires 4 x "AA" batteries (not included) & remote control requires 1 x "23A" battery (included)
Suitable for indoor use in rooms, entry points, lobbies, offices, reception areas, garages, barns, sheds & more