Hi Tom C. You mount the transducer directly to the transom but be sure to use RULE Elastomeric to coat the screws well and seal the mount. The screws will hold fine unless you strip them out. Even then you can repair easily. I'm not sure about your gps antenna question so I'll let someone else address that. BTW once you have your Triumph hull ID number please register an account with us for a free 1-year Captains Club Member subscription. Congratulations on the new 215!
