You will need to locate the pipes in your attic obviously to measure them and know what level of difficulty you will have in covering them.
Lines in attic copper.
The attic space it s in is much smaller with no outside vents and no sweating little copper lines.
After making the connection all pex fittings are installed with a crimping tool eliminating.
You should know what is acceptable in your area.
The most common gas piping is black steel.
Connecting to a copper line under the slab will require that a copper to pex fitting be soldered on.
This is why i m thinking the upstairs handler is exposed to much more humid air as it can enter the attic space the unit is sitting in which may be contributing to the sweating lines.
You want to create a vapor barrier to keep the humidity out and away from the pipe.
That should fix your problem with the sweaty copper pipe.
Line the split up and make sure the adhesive glues the rubatex split together.
Find out where the pipes are located to see if a ladder is needed to reach them or if you will have to work on your knees installing the insulation.
In other areas the use of copper is widespread.
A good example would be when running liquid refrigerant line through the attic area where temperature often exceed 110 f.
For other homes the pipes might be located in the walls or the roof rafters.