When you get it off--here is what I did.
Get a 1/4 inch stainless steel plate that will accommodate the location of the holes on the trolling motor base plate. This plate will be your backing plate for the trolling motor inside the tight space you mentioned above. Mark where the holes need to be located-- drill and tap them to fit the stainless steel "hex" head bolts that you will use to attach the trolling motor bracket to the boat(this is why you need a 1/4 inch SS plate --to have enough thread to hold, and not aluminum as it will strip). You will need two sets of hands to do this. Slide this plate in place, line the holes up(may take some time for this step), and bolt it all together. I eventually epoxied this plate in place so that I could install and remove the trolling motor bracket by myself. Don't do this on your initial install as so mods may need to be performed on the plate. This plate has been in place now for 12 years, and many removal/installs for the trolling motors either new replacements or for repairs.