With the refer off and cold test to see if it's still cold in 2 hours, many will be. Overnight maybe to long. If the truck charge line doesn't disconnect with the engine off then add a relay. Now you know your needs.
The best answer is to measure the RV drain (which may include more that the refer) to determine a course of action. More batteries is likely the best solution since solar doesn't work at night. Also guessing you have a small solar setup that is mainly for storage to maintain the battery.
Guessing you have a single 12V car or marine battery, hence about 90 AH. 2 GCs would provide about 220 AH. Additional batteries can be in the truck bed.