Talk:Doug's Projects
The cross-training perk would work well for Doug, since he has been working a lot with Marie, and it would only cost 30 IPs, which is a readily-attainable goal, especially considering you completed the character background (which will earn some bonus points).
SCUBA gear might be hard to come by in Elma, but a resource-gathering mission to Olympia might yield results.
Outside of using alien tech, using pre-fabbed components like shipping containers seems like the best bet to me, too, and probably the only low-tech means of creating habitable space underwater available with Doug's limited resources, plus, shipping containers are readily available, especially since there is a train yard nearby and with Doug's other weird hoarding behavior, adding a bunch of metal boxes to his collection probably wouldn't set off any alarms...until they started disappearing.