First, again, make sure the propane tank your grill uses is full. The ribs will be cooked low and slow, and the process will take a bit more than an hour.
Please turn on the grill, and then preheat it to 300°F. The temperature should be uniform throughout the whole process. The goal is to make sure the ribs are perfectly cooked.
Since we want to cook them using indirect heat, let's say you're using a gas grill with three burners. You can turn on two burners and leave the middle one turned off. This will provide enough heart for the ribs to be cooked entirely.
Go and get the pan with the ribs, and place it on the grill. Cover it, and let them cook for about an hour. Remember that the temperature must be uniform, so try to keep it at 300°F.
You can check if the ribs are cooked using the meat thermometer. To do this, you must insert into the center, or the meat's thickest part, far from the bone. If there are 145°F on the thermometer, they're safe to eat.
However, note that since we're cooking them slowly at a low temperature, the temperature will be around 180 and 190°F. Don't worry; this is great, as the meat becomes more tender.
After the ribs have reached the said temperature, remove them from the pan and place them on the grill. This is why we told you to make sure the grates were clean! Also, make sure the heat is still at low levels.
Get a small pot and start mixing the marmalade and apple cider vinegar at medium heat. Combine until they're well-mixed. This process doesn't take too long, only about two or three minutes.
Coat the ribs with this sauce, then cover the grill, and leave the ribs cooking for five minutes extra. Repeat this once.
It's time to remove the ribs! Remove them from the grill, and place them on a cutting board large enough. Let them cool for some minutes, and they will be ready to be served. Cut them as you please.