Never get the built in transducer!
I had a 101 for 3 years that the built in transduced and it was a PIA. Lost the bottom all the time and had a lot of interference. I run a HB 998c on the bow and spent a year consulting HB trying to get it to read right.
I finally just installed an external transducer and it worked perfectly. I installed a new 112 Fortrex in July and ordered it w/o the US2 and just used the external transducer and it works perfectly.