Dennis, Steve
We have a Lowrance set up on our Aquafish. LRA-1800 radar with the older LCX12C display and a separate HD fishfinder. Nowadays the HD fishfinder is integrated into the new HD displays, I believe.
The LRA-1800 Radar is the traditional older style pulsed radar, so you might want to consider going for the new Lowrance Broadband radar, which is the same as the Northstar radar that Oli is thinking of fitting, and uses FMCW technology with the pro's and con's mentioned in previous posts in this thread. The main con's are that it is relatively unproven technology (so there may be a few software updates to remove bugs in the first year), and there are some doubts about the mid to long range performance.
On our boat the LRA-1800 performs very well, but it does need to be properly set up and tuned to perform properly, and the set up process is a little complicated if you do not know radars at all. The new broadband radar is supposed to require very little set up and tuning, so should operate well straight from the box.
So, the choice is old and traditional with known performance, but needs proper tuning, or new broadband which is easier to use and set up, but the performance is unknown and there is likely to be a few bugs to content with.
Regarding transducer for the fish finder, we use the standard transom transducer but have fitted in the central bay under the batteries, so it is operating as an in-hull transducer. We have it mounted in an oil filled plastic box that is bonded to the floor. The performance is great. I can post some pictures of the box I made.
If you go for the LRA-1800 radar I can set it up and tune it for you, if you have any difficulty setting it up.
cheers
Bob