What is the lightest Double Slide out Truck Camper?

I don't know. Wouldn't it be more important that you like the floorplan and that it works well for your requirements?

For a start you might look at the buyers guide over at truckcampermagazine. That is, if you consider buying new.

For used campers ... supply is low and it is difficult to find a specific model.

And as always: the sticker "dry weight"'on most if not all campers says little about the wet weight loaded.