I need electronic guidance...

[Hammerhead]

I need to ask the guys who understand electronic crap for help...

Here's the situation.
My trailer has a Honda pony motor that runs the hydraulic system on the trailer.
The Honda is electric start.
I've just recently replaced the motor box and have had my lifetime fill of garden tractor horseshit batteries that don't even last six months! So I extended the motor box dimensions by a couple of inches, shifted the motor ahead a couple of inches, and had room (barely!) to mount an automotive sized AGM battery (I forget the actual group size) in the motor box! I am VERY happy that I accomplished this, and this battery rips my new Honda starter over like it's on NOS, life is good...I've been pull starting for several years.
So now that I've actually got a decent battery system in my trailer, here's what I want to accomplish;
The Honda doesn't run everyday. In fact, it sometimes doesn't need starting for a week or so at a time...
I want to protect and extend the life of my AGM as much as possible, so...
When my truck is running down the road, the blue No. 7 wire is always Hot. It powers my strobes as well as my Air Weigh scale system.
I have wired a junction box into the new motor box, that the Hot line & ground runs into. I currently have a switch, that connects the Hot line to the positive battery post and the ground is direct/constant. I turn the switch On to "trickle charge" the AGM.

My questions are;
When I turn the switch ON, am I actually trickle charging the AGM?
Can I install a diode or something that will trickle charge the AGM instead of the ON/OFF switch? I ask this because I have found because the switch is wired to the AGM and reverse powers the ABS system of my truck, if I forget to turn this switch off at night, it throws an ABS code on the tractor at morning startup.
Also, I don't want to slowly draw from the AGM overnight when I'm a dumbass and forget to turn the switch OFF at night.

So please help me...what am I looking for?
And how do I do it correctly?