Starting/Deep cycle battery question

I am tweaking my Alumacraft Lunker 16 w/50hp merc into a fishin machine and am planning on replacing the Endura #30 transom trolling motor with a Maxxum 40# or 50#. My first thought was to put a Trojan SCS225 deep cycle battery in the transom but after thinking more about it I don’t like the idea of adding another 66# to the back of the boat(tiller). Then I started thinking about replacing the existing starting battery with a dual-purpose start/deep cycle battery(27TM) instead. I backtroll a lot, and fish the St Croix and pool 2 mostly.
Good idea or no?
The deep cycle only battery weighs 66# and has a reserve capacity of 225 minutes at 25 amps. The combo battery weighs 50# and has a 160min reserve capacity. I realize I’ll get longer run time with the deep cycle only, but will the combo battery be an acceptable compromise?

I would get the second battery if your going to be using the motor alot in current. Your big motor only charges at max amps at WOT. If you go with the DP battery, make sure you charge it after every use.