by "two nights" how many miles do you mean?
the first 20 miles has very little water.
at mile 20, Lake Morena has water and a place to camp.
unless you absolutely Must start from the border, I would start at mile 20, Lake Morena, or mile 26, Boulder Oaks Campground, and head north from there for 2-3 days. The 35 miles north of Boulder Oaks is very nice and slighlty higher elevation, with a few more water sources.
also, what kind of experience are you looking for, how remote, etc.
Lake Morena actually has a small town next to it.