If you had low voltage the fridge would struggle to run, if the voltage is under 10.5 volts then it may try to shut down, I would check the voltage at the battery, When you are plugged in the power converter should take the AC voltage and make the DC voltage to charge the battery. IF the battery is not charging plugged IN then it could be a power supply issue, power converter issue or tripped breaker/blown fuse near the battery. Many times on the charge line from the converter to the battery they will use some fuse protection, as a general rule that would be 18" from the battery, so something to check.
When you run the truck it may throw a slight charge to the battery but not like when you are plugged. So it might be hard for items to run.
IF it is sparking and you have GOOD voltage then I would remove the outside access for the fridge, get an air nozzle and blow out the burner tube really good, that sits below the electrode or what sparks, sometimes bugs and debris can get into the burner tube. If it is sparking and the voltage is good it could also be a LP issue. Go to the main tank shut the valve and then slowly open it back up, if that valve is opened to fast the regulator can lock up and you might not get the proper pressure....
Hope this helps, if you have more questions or concerns please feel free to contact me, follow ups are included. Please keep in mind I only get credit when you select a rating at the top of the page..... Robert