Maybe you're going to the wrong installer? I'm all for fishermen knowing their rigs, but a lot of people seem to go about it haphazardly.... this is electricity at sea we're playing with here, the equipment is expensive and you rely on it to get you home safe. 80% of the calls I take for "faulty equipment" boils down to bad connections, overloaded circuits and improper mounting locations. I just spent the better part of an evening troubleshooting a poorly done, self installed Radar/chart plotter/ sounder system. By the time I'd replaced the damaged components I could have just started from scratch and done a proper installation for less money.
If you're boat savvy, willing to research, know ohms law, can test a circuit and know how to make a proper heat shrink connection with properly sized connectors and wires, then 100% do it yourself. If you aren't and want reliable electronics, hire an installer, hang out with him while he works, learn about your boat and expect results like this: