18 is amazing! I've never heard of a Ridgeback living that long. Don't worry about over sharing: I anticipate having a very rough time when I lose mine. The decision to put them down will be excruciating for me. When late getting home from work, my wife says that our male lays sunk down on the floor in depression waiting for me in front of the door to the garage until I get home. It's hard to lose a friend whose happiness comes from being with you: I don't have people friends who are that devoted.
My male (Fargo) has ridden with me several times now, and he's taken to the Jeep. He'll look out the rear windows and come up closer to me than he would in the Expedition: he wouldn't venture up into the second row on that vehicle. Now, he comes up between the front seats when I'm at Sonic and can drool all over the center console. The cargo liner stretches tight over that gap between the seats, and he can stand there without sinking down, but I'm gonig to keep an eye on it.
I'm sorry to hear about you losing your 13 year old: that's a good age for a Ridgeback, but it's always too soon. Obviously, we're nearing that point as well, and we dread it. We've had the male since he was 8 weeks old, and we adopted the female from our breeder when she was 6 years old. We love them both, but the male and I are especially close. He loves to go for rides and long walks while she prefers to stay at home with Mom. I haven't put them in the Jeep yet (I probably will this evening). I installed my cargo liner earlier in the week, and I hope that they'll ride up closer to me in the Jeep. They always stayed toward the back in my Expedition.