Dani, thinking about the lightest KARA today....I don't think anyone has built one lighter than 60 or 70 pounds. I think it is possible to make one much lighter if the builder kept the context, but stepped away from the plans. As designed the KARA is way over built for most hunter needs. However, that makes it really easy and fast to build using simple hardware store materials. Someone on here used a CNC router to cut out his frames from plywood and that might by the lightest Hummer so far.
If I remeber the early days of the Robber the folks that built them mentioned that they were kind of unstable under them and did not, or could not, stand up and pole them as well as a Hummer. Here is Rob Taylors Robber build from 2007:
http://duckboats.net.nmsrv.com/cgi-bin/forum/gforum.cgi?post=5820
You can see just how massive the frame is for such a tiny boat. Its way over built for what it is. Rob appears to paddle it sitting down and does well.
The KARA frame lends itself to being used as a construction frame for a strip hull, or even a cold molded thin plywood hull. The as designed 2x6 frame of the KARA is not needed if the builder relys on modern fiberglassing tech and simpler internal support frame construction.
Ever since my foam boat experiment I have been thinking about a cedar strip KARA Hummer. I think I will build a small flat bottomed garvey instead to go with the small mudmotor, but a cedar strip Hummer would be fun.
As mentioned you can also look into the Hybrid boats. They are easy to build, but are not easy to paddle - kind of like paddling a john boat. I built a similar boat of my own design some years ago. It works well. It is the largest boat I could build out of two pieces of plywood. It is very stable, and I am a very unstable person - never learned to skateboard as well as my friends. Its also real light at about 65lbs, but its width makes it awkward to handle.
If you like the way the Hellbender boats look you should check out the CLC Mill creek 13 style of decked recreation kayak. Similar to some rec plastic kayaks, but home made. Might not work well with dogs.
http://www.clcboats.com/shop/boats/boat-plans/mill-creek-13-stitch-and-glue-recreational-kayak-kit.html
DN Goodchild publishing sells lots of old boat plans and designs. There are several older frame style double ended boats similar to the Hellbender.
http://www.dngoodchild.com/divide_for_small_craft.htm click on the hunting boats at the top and it will jump down the page to duck stuff.
#5088 Broadbill is very similar looking to the Hellbender.
#5665 Featherweight is a really stubby and wide boat at only 8 feet - looks like an Aero Craft ducker doesn't it.
#5268 Pintail is another double ended boat.
http://www.dngoodchild.com/5268.htm
#7849 is another great looking little boat.
#7878 the Guenther Garvey is one everyone needs to check out just for the photo of the guy driving like a boss.
http://www.dngoodchild.com/7878.htm
All these old plans are from the time before quality fiberglass construction materials. They needed the frame to glue and nail the plywood to. From my view they can easily be built using stitch and glue and good glass inside and out. Using thin okoume plywood (4mm), then 4oz glass outside and 3oz indside you could easily have a 50 pound or less boat. The hardest part would be making sure you have the deck frame support well thought out. The dogs will be climbing up there and you will need to build that up with framing underneath it.