Hey everyone, figured I would post my experience with this process to help anyone else that wants dual batteries and wants to know how to do the big 3 upgrade.
I searched for a while but never really found exactly what I was looking for, so hope this helps someone else.
So essentially, the problem that necessitated this upgrade is snowplowing. The Meyers E47H I have drains the main battery really quickly and bogs down the truck because of that drain. Plus with running the radio (stock), headlights (either plow or regular) and blower motor and all the trucks stock electronics, I ran into some lagging alternator issues.
I thought about throwing a higher amperage alternator at the problem, but after reading experiences of others on this site (from car audio issues primarily), I decided to do the big three upgrade.
The truck came from the factory with dual batteries, so I don't have any part numbers for the trays and hold downs or whatever. The truck also came from the factory with a keyed-hot solenoid to charge the secondary battery. I have never thought that sucker worked well and the positive (charge) cable was some pathetic 6 or 8 gauge cable stretched across the firewall (6' at least, talk about loss!).
The alt charge gauge would routinely go from below 14 at idle to less than 9 volts under a load (raising or angling plow with all the other electronics on it). Time for an upgrade.
Anyway, I figured this would also be a good time to upgrade the dual battery system as well.
I also looked around at isolators, solenoids and other systems on the net. I found Cole Hersee isolators seem to be the best, but HellRoaring also a contender. There are tons of choices out there, but after some research (and help from Boarsheadburban), I decided on a solenoid version.
The Painless wiring kit 40102 served as the guinea pig for this endeavor, because I wanted the "switchability" between linking the batteries together.
With the Painless kit, you can choose between having the batteries not linked together, linking them together for charging and starting and also link them together when the truck is turned off (for things like welding and winching or hooking cables up to your nipples or whatever).
I'm sure there is someone who will ask "Why did you only use 2 gauge?" Answer: I saw some posts of people using 1/0 or 0 gauge cable and that's great, but after seeing the difference between 0 and 2 gauge cable in the store, anything is going to be an upgrade from stock.
Price breakdown of parts:
Painless wiring kit: $120, Summit Racing
Connectors:
Battery side terminal upgrades, $2 a piece, 4 total = $8
2/0 gauge terminals, 10 total, avg price $3 each = $30
2 gauge welding cable, 25' (6' extra when all said and done), $45
Heat shrink: black and red, $5 each = $10
I think that's it. Grand total: $213 (give or take a few bucks).
I saved a few dollars on replacement cable and stuff becuase I reused some of the cables from the old setup, just threw new connectors on them and tested for resistance. Example being the feed from the + main battery to the distribution block.
So onto the actual process...

A pic of the shopping list.

A pic of the old setup (little cables and junky connections, especially grounds). The plow wiring is a nightmare jungle with too much wire.

Bad grounds. What you can't see is the broken block to frame connection.

New 2 gauge cable.

New charge wire (from alternator to + main battery terminal).

New ground strap from back of block to frame (old one was broken and dangling and not connected).

Painless wiring switch mounted. Green light means both connected for charging and starting. Red light means both batteries connected when key is OFF (that's why it's RED, to alert you!).
I am thinking of labeling the lights and the switch, but need to find the right font and stickers.

New dual battery solenoid mounted. I originally mounted it too high near the overflow tank, and did a little arc welding when I tried to close the hood.
I had to move the sucker out of the way, a bit lower and on the angle because of the silly hole in the fender for the OEM intake system (which is long gone

)

Completed main battery terminals.

Completed main battery grounds (there is also an unpictured one going to the block near the t-stat).

Mr. charge wire.

Aux battery wired up and ready to rock out.

I cleaned up some of the wiring for the plow and plow lights as well as the feed wires for the painless dual battery solenoid and the charge wire to the aux battery. Just used hydraulic hose clamps screwed to the firewall. Works just fine.
Still some random wires out there to be cleaned up, but everything works like a charm.
I cut out a lot of steps here because the process isn't that hard. All you really do is take one cable off, measure the new cable and add the connectors.
This upgrade is WELL worth your time and doesn't have to cost as much as mine did, but it was still cheaper than a new HO alternator!
Thanks for reading, keep up the great

community! ! ! ! ! ! !