This is just my opinion of course but I do not see any advantage at all to mount a trolling motor into the mirage drive well.
There are plenty of posts on here that show how to make motor mounts for TI's, and also island hopper sells them if you don't want to make your own.
Once you have a motor mount you can mount any motor you like on the boat, if it was me I would go with the cheapest possible (like under $100 dollar motors at Walmart). Basically you would keep the motor tilted up on the back of the boat, then just swing it down when needed. If you have a trailer there would be no need to ever remove the motor or batteries from the boat (that's what I do with my outboards, the just live on the boat and have never been removed).
99% of the time the motor would be locked straight, and you steer with the boats rudder. If the rudder were ever to break for some reason the motor becomes your back up steering.
Yes you can get huge batteries for more range, but the way you discribe your needs, one or two 25lb ATM batteries will probably do you just fine, again if you have a trailer they never need to be removed from the boat. I would just store them on the rear deck in battery boxes lashed down.
Of course you can get as fancy as you want with I-pilot remote control systems and such but why....you just using it locked to get you in and out of harbor 99% of the time. If you want to drive from the front seat it's pretty easy to make a tiller extension that reaches up to the front from a piece of $3.00 PVC pipe (that's what I have).
90% of the time the motor will be just tilted up harmlessly at the back of the boat, you can just put a bag over it to keep it dry (that's what I do). I have seen quite a few people using fresh water motors in salt water, as long as you rinse it off well after each use it should last a while (not forever though, but you will likely get a few years out of it as long as you rinse it every time).
The TI is only a couple hundred lbs and glides easily in the water even a 30 lb trolling motor will push a 16 ft 2000 lb bass boat with ease, one misnomer about trolling motors is people buy a 55 lb thrust motor on small boats thinking it will go faster, in reality you don't go faster (well maybe 1 mph faster), but you use much more battery power way faster. Most cheap trolling are most efficient at near full throttle if operating at 1/4 throttle you are just wasting the battery dumping the excess power into resisters and heat sinks unless you have a fancy pwm controller (only on the expensive motors). Yours will be either on or off, you won't have a big need to crawl very slow (like trolling) you are just using it for basic propulsion and that's it.
If it was me I would just get a 30 lb walmart special motor for under $100 bucks and adapt it to work. A home made motor mount is only $15 bucks in materials (plenty of posting on how to make).
Two ATM batteries will be about 50 lbs, and the motors are about 15 lbs, you don't notice that extra weight on the TI at all. Actually mounting everything aft actually helps on a TI (you want as little weight as possible in the front of a TI FYI).
Besides, if you get a mirage slot mounted motor, where in the heck would you put it when your not using it ( nobody has thought that one thru (lol)) plus you lose the use of the pedal drive (the #1 feature of the boat).
Keep in mind the TI is the fastest kayak out there and glides easily thru the water with just one peddler, with two peddlers pedaling lightly it is faster than your trolling motor, plus they can pedal all day long with great ease as long as you carry extra fuel (a couple twinky's and some water lol).
Hope this helps
I posted the reply before actually clicking the link, I thought you were pointing to the Island hopper mirage slot mounted motor option, which is way more expensive and as I describe above, is not well thought out (where would you put it when not using it...). Actually the salt water 30# version you pointed to for $199 looks to me like a pretty good deal to me (if you go in salt water).
In another area of their web site ( http://www.islandhopperoutboards.com/ka ... hobie.html
) they sell complete kits specifically for the TI if you don't want to make your own motor mount (the motor mount is the key to everything).
Here is a link to a video from Tom Kirkman using an 18 lb thrust motor that is worth watching
Actually the transom mounted version with remote control looks interesting also, if you mounted the motor slightly to one side it would easily clear the existing rudder (http://www.islandhopperoutboards.com/ka ... dders.html
), kind of like the Torqeedo 403 setup.
I had an Island hopper gas motor (same company) on my TI for 3 1/2 yrs before switching to a Honda, they are a good outfit, and have pretty good stuff in my opinion.