I'm a big fan of the larger, multi-part puzzles. Now that I can marvel in my own mind-bending magnificence with the Perpetual Testing Initiative, is it possible to install autosave points into a level I have created?
No, its not. You have to use the Portal 2 SDK, as the Auto Save is an object.
The Perpetual Testing Initiative is for maps you release for the community, and are meant to be small enough that you dont need auto-saves (As auto saves are mainly used with big maps that have 5 or 6 rooms / chambers)
You can however upload maps made / edited in the Source SDK's Hammer Map Editor to the work, as part of the PTI
(Thanks to Richard Benson for informing me of that)