they seem to last a lot longer if the rubber isolation mounts that come with them are used,when mounted solidly failure happens quick most of the time.

I couldn't imagine running any ignition box without the rubber mounts however I've had two msd in my muscle cars for years and no issues however they are older 15-20 years old now. Not sure if it's where it was manufactured or if boats just don't like them. Lol... think it's hit and miss honestly. Most people I know that have run them in boats over the last 5-8 years or so keep a spare in the cabin. Personally I'm purchasing Daytonas as I've yet to hear of one failing and have the features that I like. If I'm not mistaking Daytona adopted the old crane boxes which for the most part everyone really liked. With SC engines especially the ability to fine tune/map your own advance at different rpm's is a must. Not just lock out at your weights at your typical 28-32 and call it good. Goes way beyond that but not without extensive testing and tuning.

So in a nutshell I can't say msd has treated me bad over the years on the street however would I purchase for new sc marine builds? No.... Heard to many horror stories and like what Datona has to offer at a good price.

Run an MSD 8222 capacitor. Brad Smith idea, voltage spikes kill boxes, especially the newer ones for some reason.

I have a Daytona Sensors™ CD-1™ Kit, Part #102003 new in the box I don't need, has all paperwork, software disc and all computer cables for tuning. Hard parts list below;
Part #102001 ​CD-1™ Ignition Module (with Wiring Harness)
Part #102002 Ignition Coil
Part #115012 ​2 Bar MAP Sensor (for supercharged applications).

That's a good to know post. I would imagine many boats have multiple stereo amplifiers that probably don't help much either. On and off throttles quickly with larger voltage output alternators etc.

how much.

Everything that has been said above. Mount with rubber, Vibrations are a killer. Also I ran all separate wiring. MSD boxes do not like variations in current. I pretty much isolated them. If they are in anyway involved with your stereo system, power fluctuation will eat those boxes. I always kept spare boxes, I saved weekends for at least 3 boats plus myself at a few poker runs. Suddenly nothing, no reason, just turn key and no spark and nothing you can do, no signs, they are podded for moisture. Have seen many race boats have spares mounted with a switch so if one dies, they can switch over the boxes. They are very unreliable. I have had MSD in 3 boats, I would not initially ever start with them. They were already installed. Not to mention the pickup, caps, rotor, literally last 1/2 of a short season and they look like they have 20 years of rust and found on the bottom of a pond and I boat in fresh water....lol.

All good info. I do recall mild thunder among others giving the inners of distributors a light coat of CRC??? Something or another and they won't corrode but you'd have to do right from the get go. I'm not sure where msd comes from anymore however if you compare with some of the knock offs you can hardly see any difference if any. I have no idea so not fair to say but... Not really anything to do with the ign box. If you do look up msd distributors the net is full of threads from various forms acknowledging the same issue with corrosion. Sounds like the coating is the ticket without a doubt. I'm going to try the Daytonas but who knows they may be no different. (Distributors).

I run the capacitor like everyone has said I also use the rubber spacers. one other thing I do is by the plug and play msd gm adapter harness that just plugs in. if and when it goes bad I unplug and plug the original pigtails into my coil and run it without it to get back to shore and I also carry a spare just in case but I have never been left stranded from one of these going bad.

The Daytona Sensors stuff retails for $700 so $375 to your door.

Rig the MSD boxes with quick disconnect wire connectors and carry spares.
Ben