I'm just guessing here but I'm assuming you have an H16, I have seen several H16's with the cheeta motor mounts around here, and those that use them seem to like them, however of the 10 or so motor mounts that I have seen on H16's I only saw one that actually had an outboard hung on it, so I'm questioning how often most people actually need or use them (may be more bother than they are worth).
We have a TI which has dual mirage drives, and we have to negotiate canals once in a while (to get across to the Atlantic side in Key Largo, and the other camp ground we stay at (mile marker 13) called blue water lagoon has a 1/2 mile canal that we have to follow to get out to open water. Yea we can pedal out with the mirage drives and that actually works ok, but we also have an emergency backup outboard (because we often go offshore), so 9 times out of 10 I'll just fire that up. It's near impossible to sail in any of those canals and paddling through them would not be fun, I have however seen people poling thru canals though with their Hobie cats (something to think about, and probably what I would do if I owned a cat). Just bungy the pole down when not using it, the one I saw was using what looked like a telescoping pool pole, actually looked pretty effortless, and they were using the rudder to steer. I think the hardest part would be learning to hum in Italian (gondola songs).
If you have the money (a couple grand (ouch)) you can get a Torqeedo with their high tech sealed battery (the battery weighs about 5-6 lbs and can be submerged. Some of the Torqeedo motors can also be completely submerged with no ill effects (you will have to verify which ones). All in I think the whole works (motor, batteries, etc) is under 15 lbs total weight, and has much longer battery life than pretty much anything else out there using 70 lb batteries.
Keep in mind any outboard if it gets submerged, the outcome could be very bad, I've tipped over more than a few times with outboards, and as long as you rinse the motor quickly and replace all the oils and stuff, they can survive.
If I owned an H16 what I would do is not buy the Cheeta mount (too expensive unless you can find a used one really cheap). I would just go buy a $100 dollar trolling motor (like a water snake). mount it behind the rear cross brace, it doesn't need to be anything fancy, you can probably use a 2x4 and some spectra string to suspend the motor back there. If you look at how an airplane engine is mounted in a Cessna, it's just a bunch of little aluminum rods mounted at all kinds of angles (no frame), you can do something similar with spectra string to hold the 2x4 motor mount rigid. Have two spectra strings tied to the lower part of the shaft then ran back to the stern near the rudders. The 2 x4 would be lashed to the rear pylon somehow with spacers. You want to be able to swing the motor up when not using it. The spectra string mounted near the bottom of the unit makes it so you don't need a substantial rigid motor mount, the motor still swings up easily.
Keep in mind we are talking a tiny motor here, it doesn't need to be super rigid, those two spectra strings going to the back mounted near the bottom of the lower unit are what take all the thrust load.
So to sum it up you will need one 2x4 about a 15 inches long. and possibly a couple more around 6-12 inches long that will be the spacers (the length depends on how much lower from the rear cross brace the motor needs to be mounted). I would then lash the tops of the upright spacers to the rear cross bar. The mount itself will be U shaped with bolts holding the upright spacers to the main 2x4. You may want the upright 2X4's mounted so the skinny part of the 2x4 is against the rear cross bar, if you cut a small groove in the side of the upright 2x4 this will prevent it from sliding up and down on the round crossbar (no need for any screws or rivets of any kind on the rear cross bar, just lashed on to the bar.)
Now put in two eyelets in the ends of the main 2x4. Now run a piece of spectra string back to the rear hull near the rudder (same connection point as the two strings attached near the bottom of the motor), then another to the front pylon (front lines are optional, you would need to untie to swing the motor mount up), do the same on both sides of the boat. The 300 lb test spectra string is what holds the whole works rigid and centered.
As far as a battery goes, they sell sealed AGM sealed batteries, if lashed down somewhere, possibly two smaller ones (one on each hull) might work better than one giant 70 lbs monster. If the sealed batteries go under water (pitchpole), it's not the end of the world, not sure about the watersnake though, worst case it will cost $100 bucks for a new one.
Your only using it to get in and out of the canal, (one battery for coming in and the other for going out).
There you go you just designed and built a motor mount for you H16 that is more than rigid enough to support a motor and it only cost you $15-$20 bucks. You can get the 300 lb test Spectra string at any hobie dealer for between $.22 and $.30 cent a foot (around 30 ft). A pressure treated 2x4 8 ft long is around $6 bucks, and a couple bucks for stainless eyelets and screws. Try and use cinch knots wherever possible on the spectra string (the stuff is very slippery)
I have twin 2.3 Honda outboards mounted to my TI using the same construction method (spectra string), and the spectra string motor mount has been in service for over 4 years now.
A couple years ago I posted a similar discussion and design with a guy on this forum who want to mount a mirage pedal drive on his H16, everything would work exactly the same, but a mirage drive would be mounted instead of a water snake. The mirage drive would have been mounted in a swing up mount. He was planning to run the pedals via spectra string to another set of pedals up on the deck somewhere thru levers. I have a similar spectra string pedal setup on my TI so I can pedal both the front pedals and the rear pedals at the same time from the front seat, just using spectra rudder string and a couple pulleys (takes a lot of leg strength though). I can't find that old post (sorry).
Sorry for the long response, hope this helps you. If it were me, before buying anything, just try poling in and out of the canal, I think you will be surprised how fast the H16 glides, just remember to hum in Italian.