[jjzepplin]

Not an expert yet and maybe never. This is a highly respectable line of work to be in. I may take some classes to get better and get a license.
As for the sweat- It's sweating so you don't have to! HAHA!
No really though, Does the unit have a good drain set up? Make sure it's dripping well at idle. And yes the humidity and amount of humidity will sweat the evap. This is how it removes condensation from your air. Cab leaks and having the outside air on can contribute to excessive condensation. I am not an expert on Vintage Air Systems but if I am right they do not have an outside air option.
Having two of the same units gives you a great advantage. Make sure both have the same readings on your gauges and basically make them the same. This is how I fixed my wife's A/C. I also had some great help from some fellas on here that provided Schematics for the electrical on the vehicle. Without that I could not have fixed it correctly.
These are bot running the SD508 right? Oh and be sure your insulation is not touching the evap. It needs good flow to Evaporate the condensation.
Probably doesn't need any if it did not come with it. It's technically a dehumidifier as well as a heat remover=by-product is the cool air. I think. I cannot even see my evaporators in the cars so they may be sweating crazy. I know my house unit sweats so much that it NOW has a steady stream of condensation from the drain. My windows are old and keep going thru the doors all day though.