Someone must have read your post :-). This feature is now available in the Nortik Duo Expedition packraft. The raft has two internal bags which are sealed with watertproof zippers. I guess that the internal pressure on the bags keeps air and water out. Found no reviews on the performance, but here’s a pic: https://www.faltboot.de/fileadmin/_processed_/1/3/csm_nortik_raft_Tasche_integriert_6b109150e1.jpg
