The smaller brother to the plane I'm building, the Rebel, with a Rotax 912 would be excellent for this type of flying. Deciding whether to build or not is a tough decision... it is going to take time, a lot of time. You might want to keep an eye on the classifieds site I host for builders... sometimes there are partially completed kits listed there.
http://www.dcsol.com/classifieds.
There are a number of older aircraft that would work well for this type of mission also, but reliability can certainly be Russian Roulette. One in good shape can be hard to find, and getting one into good shape can be very expensive.
There are certainly other experimental aircraft that might fit the bill, but you might have a hard time getting a load of fish into most of the 2 seaters on the market. The Rebel really has a lot of room in it that would make it perfect for this mission.
Murphy Aircraft has some good information on their web site right now about the Rebel as an LSA aircraft.
http://www.murphyair.com/
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