To install normal stuff on positive ground if designed for new ground is a problem as most use common chassis ground.
You can check with manufacturer as some may be compatible but not likely.
They do make DC TO DC converters just for this and they may be hard to find but should not be too expensive.
They basically make a floating 24 VDC that puts the output voltage 12 volts the other side of ground so to speak
Just verify correct application as most are for aircraft 24 volt systems to allow 12 volt equipment.
Tony & Lori
1989 Country Coach Savannah SE