I cut the foil at one end so that both chambers are still joint directly.

Then I glued both chambers at the boundaries. Now the dildo can be placed between two chambers filled with water.

This is a detailed view of the entrance. The amount of water has to be choosen accordingly to the size of the dildo.  It schould be fit in tight. Use lubricant for testing!

This is a detailed view of the entrance.

The entance has rather sharp edges, so an improvement will be to flip the edges around and glue them.

This is a detailed view of the entrance border

I glued three chambers together and one Zipper at the end

I glued the zipper at the other side on the other end  to close the circle

This is the top view, the zipper is open

This is a top view. Inflated with water

Another top view