OK, I found what I was looking for. Battery Mart sells the plugs with wires that mate with the ones in my picture above. I ordered the lug harness which has battery ring connections on one end, a 3 amp fuse holder on the positive wire side and a plug on the other end. It is labeled DEL-LUGS and sells for $5.95. I also ordered a male cigarette plug harness labeled CIG-PLUG for $5.95 which has the same plug end opposite the cigarette plug. They work in conjunction with the BatteryMinder and the Battery Tender units.
I already have a ring terminal connection attached to one of my batteries for when I want to connect the BatteryMinder unit such as during winter to keep a maintenance charge on the batteries. This wire sticks out the top of my battery compartment and has the protected plug on the end. My idea is to cut the ring terminals off the newly purchased lug harness, run those wires into a weather protected box temporarily mounted on the frame and into a solar controller inside. The molded plug ends can then be connected after I run the + and - wires from the 20 watt solar panel into the box with the solar charger. There must be some ventilation within the box but not where water will get into the controller. The cigarette plug is just an added perk to connect somewhere in the trailer or a vehicle should I ever need it.
Note that this is not a permanent connection. I already have a 5 watt Solargizer charger/maintainer in use that has done a great job of keeping the batteries up to snuff but I plan on putting a greater load on them in the future when boondocking/hunting. I want to be able to disconnect, pull the 20 watt solar panel off the roof/awning and place them inside when I leave the unit and go home for a few days.
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system