1st Gen Tacoma - Wiring a solar battery tender?

I've got a 1st Gen Tacoma that doesn't get driven very much and the battery goes dead after about a week or so of disuse. I've been starting it once a week and letting it idle for a half an hour or so to keep the battery charged, but this is getting old.

So I picked up a solar battery tender that plugs into the cigarette lighter. This would work fine except all of the cigarette lighter/accessory plugs are switched with the ignition and it requires a constant power accessory socket.

So I'm trying to figure out the best way to make this work. My first thought was to use an Littelfuse "add-a-circuit" to piggyback on one of the other fuses in the internal fuse block and add another accessory/cigarette lighter outlet, but I'm having trouble finding a fuse that is constant power. Additionally, I'm not really sure this is the best way to accomplish my goal.

Any ideas/tips on how to wire this thing up?

EDIT: I suppose I could pick up a cable to direct wire this thing to the battery instead of using the accessory socket. I wonder if this might be a better route to take. I'd need to figure out where/how to get through the firewall though.

 

It would be easier IMO to get a SAE connector and mount it on ring terminals to the battery and connecy it to the panel when needed. I do have my dash cam tapped into a constant power fuse. I'll post it up later when I get the chance.