As I said earlier to get at the switches on the panel the fridge needs to be removed from van, I haven't read the Instalation manual that well to date, thats the best way to find out ........... but you will have to unscrew the gas line, gently, disconnect the 12v cables (turn van battery off) unplug the mains lead and pull it thru the hole in wall, fixing screws you need to refer to instalation manual..............
Give 12v a miss too mush stuffing around hooking up to tug, though my fridge has an anderson plug for power to fridge from tug, so I can use a Anderson jumper lead and plug into van supply, with my solar I can run the fridge while the sun shines, no sun probably get an hour or so before killing battery....
Advised to select gas, walk away for awhile then return and try to start on gas, remove lower vent, if its dark you will see the flicker of flame and while removing the wind guard from burner makes things more visible its easier to just use you hand on the bottom of the flue, if its going, it will be warm/hot, give it a minute or so though ... My money is on selector switch being frazzled and sounds like your fella will be more than capable of seeing if the switch is stuffed, secret signs are smell, the black and white wires from switch are the 240v so if they are sort of darkish then thats also a sign it cooked ...........
Anyway if you haven't got an installation manual go here
https://epi.dometic.com/externalass...S*MTcwNDI2NTE2NC4yLjEuMTcwNDI2NTE2OS41NS4wLjA.
It will download a pdf manual for your fridge ... from the Dometic site..... so look at it before you start pulling things apart ...........
Leave you with what sounds the capable hands of your young fella .................. Hope to hear good news in the future.