I own a 16ft Sylvan tiller.  My original setup was a 40 hp for Erie, and I would throw on a 9.9 hp kicker (from my previous 14ft) when I fished the local restricted hp lakes.  For my size boat, the 9.9 kicker was too cumbersome.  Approximately 10 years ago I sold both and bought a 20 hp for all scenarios.
 
As I age, I have become less of a risk-taker and have considered getting some type of insurance for motor failure while fishing Erie. One option is to install an emergency back-up motor when on Erie.  Since my main motor is only 20 hp, I want to keep the weight as low as possible.  Online, I have read some have installed 2.5hp kicker (31lb) on similar sized boats, but I question if this little motor would achieve my goal.  If I knew I could get 5mph I might consider it.  Any experience you could share would be appreciated.
 
Another option is to buy a towing membership for $95 per year.  Just seems like these towing memberships were not meant for a 16 footer on lake Erie.  Anyone have any experience with Lake Shore towing?  Response times?  Any unexpected costs?

We don't have any experience personally with getting towed off Lake Erie...
But I have heard towing response times from "Johnny on the spot" to waiting several hours on "busy" days.
 
Can't give any advice on Lake Shore's towing policy, we have a Boat US membership that covers towing and also our boat insurance covers towing too... the difference being that Boat US pays the towing company, our boat insurance requires us to pay the towing bill then submit the bill to them for repayment.
 
One strong word of advice that I can give is...if you don't have a marine radio - GET ONE! 
You can't rely on cell service on the lake.
Not one of those battery powered hand held ones...a real radio that is mounted in the boat and a GOOD antenna - like a Shakespeare Galaxy series.
Lots of time you can put out a call that you're motor is dead and you need a tow and a "good Samaritan" will offer to haul you in... we have towed several disabled boats to the docks.
 
Also, just my personal opinion on the kicker size... any "back up" motor is better than no back up motor! - it may just be enough to keep your nose into the waves if a storm kicks up while you're broke down!
 

Erie Mako,
Thanks for sharing your advice, and opinion.  I had reservations about submitting my post, since I thought I may get critical responses stating my 16ft/20hp setup doesn't belong on Erie. 
 
I definitely have to pick my days in regards to the weather/waves and I stay within a couple miles of shore.  This small slice of Erie still provides me good fishing in May and June.
 
 
 
 

We see a lot of small boats out there, you just need to use good judgement on when to go and when to stay away!