Yep, your dad should be able to do it no probs.
My hubby just made a duel ended extension, that is only about 1 mtr long. That way we plug it onto the end of our regular extension if and when we need it.
Clover, with gas fridges, there are a couple of things I have found that improve them greatly.
1. Make sure the fridge (and therefore your van) is level.
2. Make sure that the vent for the exhaust is clear and that nothing is leaning against it. I have actually taken the external cover off ours. Also our van door opens and folds back over then vent, so I just make sure that the door isn't hooked back over the vent all day.
3. They struggle to cool a lot of stuff at once. So don't get to where you are going and then go buy a heap of groceries and put them all in. I try and buy a couple of days worth of meat before we go and pre freeze it at home, and I try not to buy bottles of warm drink and put them in.
4. We use an esky with ice for drinks/snacks that the kids need to access constantly. I just put the days allocated snacks in there. It's keeps them out of the van during the day and I know that all of my "good" food doesn't warm up.
Gas fridges can be great, but they do take a little bit of pre planning.

We are now in Daylesford in Victoria. My sister lives here and we are in her backyard.
We arrived in Yarawonga and camped by the Murray the Tuesday before Xmas and stayed there for a week, but with the predicted high temps today and Tomoz, we headed for the hills for a drop in temp (just hope we don't get any fires!)
Then on Sunday, we are off to the melb zoo and then down to the morning ton peninsula to visit some friends for a few days. We head back to Qld later nxt week.
Not looking forward to going back to the heat :/ it has been lovely down here.