For those OpenROVers located in Europe, I can recommend this glue:
I sucessfully glued the inner structure and the e-chassis with it.
It is based on acetone (much less toxic than dichloremethane) and therefore it takes longer until full stability is reached (up to 24 hrs). But this was no big problem during work, since initial stabiltiy is reached after a couple of minutes.
It's crystal clear, water resistant, very robust (acetone also welds the acrylic components together) and it already comes in a bottle with a needle!
I did not try to glue the end caps with it yet - before doing this, I will make tests with some spare acrylic.