Building a two piece barge - Ideas?

Here is what I would love to be able to do, can anyone give me Ideas, and things to think about along the way.
What I want is a barge that will be able to carry a Mini Excavator (8000LBS) Mini Truck/Large UTV(1600LBS) large tandem Axle Trailer with sand (8000LBS)
In other words, something that can safely carry 20-25,000LBS.
Now comes the tricky part. I want to trailer this on the road, so each "section" cannot be over 8'6 and I don't want it over say... 38' long.
In my head I would like to take two crafts almost identical that are 7'5" wide by say 36' long. Each one hopefully weigh less than 10,000lbs (I don't think that is too much to ask is it?) Better than that, I want them to have their own "on board" trailer system (a set of axles that can be lifted up out of the water after launch) Once in the water I would want then to ‘pin’ together (This could be done with large square tubing into custom slots on the deck) in such a way that the large heavy loads become very stable. The idea would be to make a “small” portable powered barge to bring the “small but heavy” equipment to remote lake islands or no road access areas. Mostly for building septic fields and landscaping.

Things that I would like to hear… (what type of float/pontoon/etc should I use),
What sort of power should I use (can I use basic outboards, have a system when the two units are together I can manage the controls easy)
I would like to have some form of a shore ‘down rigger’ setup so unloading on a rocky shore does not have me rolling the backhoe into the lake.
Things I don’t want to hear are that it cannot be done, it can be done, I want to do it and this is just bouncing a few ideas around.