My shop is a distributor for the Precision Temp line so I can only speak for that brand. The RV 500 is very popular with my clients. They all seem to want them installed over the standard units.
This unit was installed in a
1957 Caravanner. The hole is slightly taller and also narrower that the original opening. We have found a plate, the same size as the door, to be the perfect solution for changing the hole. It is not seen in the photo but 1" x1 1/2" x 1" ribs were bent and riveted to the patch to give the screws something to bite into and to firm up the outer skin.
We installed a salvaged eyebrow to help make the unit blend in visually.
This one is installed in a 1971 Overlander. They offer an unpainted aluminum door that can polish up just like the skin.
The feed back I have gotten is all positive. There are some disadvantages however; To work properly, the water must remain on. Navy showers to conserve water do not work well, as a constant flow of water is needed for the unit. When boon docking, this is not the best at conserving water. The other disadvantage is disposing of said water. If hooked up, no worries, but if not, you need to be able to hold back the waste water.