Have you got one of those little thermometers that look like a travel clock? I consider this one of the best investments for anyone new to camp oven cooking. Think of your home oven - the first thing you see in a recipe book is "pre-heat your oven to BLAH temperature" Well, it is the same for the camp oven - but you can't turn a knob to the required temp. The thermometer will tell you when you have reached the temp.
If you use one of those inside the camp oven (before you put the meat in) you can get the right number of
heatbeads for the temperature you need for
that particular oven on that particular day (chilly wind vs hot sunny day etc). Then you know the meat is going in to an oven at the right temperature and you don't have to check it for at least an hour. Sometimes you need a bit more heat underneath rather than on top.
Leave the thermometer in the camp oven with the meat - when you check the meat you will see if the temperature is starting to drop off or holding steady. That will help guide you about whether you need more beads or not.
Remember though, each time you lift the lid the temperature inside the oven drops, so you have to add extra 5 minutes or so for the temp to come back up. If you are checking every 20 or 30 minutes, the meat could be cooking at 120° the whole time instead of 180° - thus requiring a lot more time to cook (but by crikey it will be TENDER!)
It's all experimenting - try this, try that - until you learn what affects your heat etc and then you learn to trust your instincts. Each time you cook you discover something new - a wetter marinade may need more
heatbeads, a drier damper mix may burn or whatever the case may be. It is a steep learning curve to start with, but worth every crunchy mouthful

When you have guests/family around, have a second small camp oven going with a damper in it. Then if you have to wait an extra half hour for the meat to finish cooking, tide them over with damper and cockies joy

One final hint - get your meat out of the fridge/chiller/icebox/esky in advance so that it can come up to an 'unchilled' temperature before you put it in the oven. Otherwise the first part of the process is the meat trying to get warm rather than cooking. If it is a warm day, get the meat out when you first light the
heatbeads. In chilly weather you may want to allow a bit more time.
HTH

The above is my opinion only and any advice followed should be done with caution and common sense.