One of the many problems with retrofitting any car, including dome cars, for isolated use (no HEP, totally self contained) is that all the toilet waste must be contained, so that takes up space under the car. The next problem is adequate power generation. While many roads installed Wukesha ice engines, that alone doesn't solve heavy electrical demands. Remember, that even with a Waukesha, heat must be available under freezing operating environments. Back then, that meant steam trainline, which is not available anymore. Hence, the need to place a engine-generator set somewhere under the car to provide both electricity for heating and cooling. One caveat was that a Waukesha set could be configured to run a refrigerant compressor or a generator. Some business cars were outfitted with one of each: a 32 VDC generator and one a R-12 compressor. I don't know what they did for heat, outside of the trainline.

What is typically done nowadays is to first remove the battery box. This is possible because while in the past, the batteries would supply car lighting and fan motor electricity when stopped (shore power when at layover), and therefore required large battery banks; today that method is not employed. Instead, either HEP provides the juice, or the engine-generator does the work. There is still a small battery case employed for emergency lighting and gnerartor starting and controls.

Now, with a toilet retention tank, there is even less and limited space, removing the large battery box is only a partial solution. Also, HEP transformers and conduit will need to be factored in. Next, the thing to do is remove the axle-driven motor-generator set, which frees up even more space and allows more weight to be reassigned. With a dome car, there is generally two seperate refrigeration plants. They will need to be renewed. The good news there is that modern plants are far more efficient and lighter than the Waukeshas. And, by removing the Waukeshas, we can remove the propane bottle racks, too. So by removing the battery box, Waukesha engines, propane racks and axle driven generators (or a combination/subtraction of any of those parts!) weight and space can be reassigned, but only to the extent that the frame of the car can handle it. Respringing the trucks to rebalance the car is also a consideration.

I don't know what the process that Holland America took, but like one person noted, the ATSF full length dome operates frequently and does not have the A/C plants on the roof. I haven't looked at what the BNSF did to make that work.