hello zettler, you sure ask a lot. if you have a front deck on the boat ( i really couldn't understand for sure but think you do but didn't want to cut into it) i'd get one of the flat round plates that bolt down to the front deck and yes, you will probably have to cut to get to where you can get under to put the nuts on the bolts. you won't loose that much styrofoam. that will be the most solid way to do it. then you'll need a post and seat. set the plate (if that's what you decide to do) back as far as you can to give you room to operate the foot control. i think walmart has all the things you would need for that. and i put my battery in the front and i keep it strapped down so it won't turn over. the 13 inch post should be enough. the swivel bracket on the boat seat will add another inch.
your trolling motor battery should be up close to the motor unless you run a 6 ga wire from front to back. that battery will last longer up front close to the motor. i've run them both ways.
your motor and gas tank at the rear will pretty much balance you out. you will have a battery back there to for the motor. i'm assuming it's electric start. and no, you won't need to strap the gas tank down. the battery yes because it could fall over and the posts contact the aluminum boat and short out. i've had that happen. i know i didn't answer all your questions and maybe didn't help you at all.
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