Looked at those Dave as I have that problem with the internal aerial on the Lowrance.
They have to be at least 1 METRE away from any vhf aerial, they also have to connect to a nmea system, and not directly to the plotter like the older style aerials. Not enough room on my roof for one .
Cheaper than the LGC 4000 they used to make, that was £400 !!
The internal aerial is fine once moving, but is a bit slow updating at slow speeds, apparently because mine is fitted flush in the dash according to Lowrance !