I would really check the car over. Flexdisks,belts,hoses, belts, etc. Plus add a little heavy oil to the outer cv joints. You could also add straight 40 diesel oil as makeup. It will reduce oil consumption at those times you may want to or have to travel faster. Longest distance AAA towing plan might be considered.

If I went alone. I might remove the front passenger seat. Using some thick plywood to make a bed platform. You may be in areas where it is not safe enough to sleep in a tent from time to time or it is too cold.

Truck stops are pretty safe places and you cannot use a tent in them. You can buy a shower there as well. Some times free with fuel purchase. You can roll your big diesel rig up to the pumps.

The car can idle all night for less than a gallon of fuel for heat. I did not want to do it but was stuck in a storm in the week before Christmas years ago. Forced to stop driving in the middle of nowhere. While driving a 240d purchase home.

I tried to outrun the storm. I was headed north and it was coming in from the west. I was trying to reach the point I turned east before it got too bad. My 240 actually did generate more than adequate heat at idle for the night.

Remember on these now very old cars you do want to add a few ounces of heavy oil to those rear outer cv joints. For a trip like this. I would add a fan belt to the spare parts list as well.

Over the years I have done many trips while trying to keep the costs of them down. I totally agree you only live once and make the effort to do the trips we used to call busmans holidays years ago.