Hi guys, mind if I join in?
I'm not sure what's killing your preamps but I wouldn't trust the coax cable anymore. Or is it just a question of quality and a coincidence?
You asked about protecting your preamps? Let me show you what worked for me.
I wrapped both of my RCA PREAMP1Rs with foil tape and they made it 5 years:
Here is the Winegard LNA-200 wrapped in foil tape, which I foolishly bought a few years ago. I guess I believe the hype and I believed that "LNA" actually meant Low Noise Amplifier" which is misleading:
I have been using Kitz Technologies pre amp and am extremely satisfied.
First I went with the KT-200. Amazing results.
Then, as soon as they became available, I got the KT-700 UHF VHF COMBINING Preamp: