For the whole wedding trip/honeymoon, the plan would be to fly to Gibraltar (or maybe Malaga), spend a few days on Gibraltar and get married there, then go into Spain and hire a campervan, which we'd travel around in for maybe a couple weeks.
Here's one site I've been looking at: https://www.flamencocampers.com/en
A few years ago I started looking into getting a campervan, but could never save up the money for one. I was really keen to do a campervan holiday though. OH had been planning to travel around Europe in a campervan too (this was all before we knew each other), so on our first date, it was one of the things we talked about wanting to do. For our first holiday together, which was about 4 months after we started dating, we hired a campervan in France, and travelled around in it for 2 weeks. We decided that we'd get our own campervan, but since neither of us are knowledgable about mechanical things, we decided we didn't want a retro one like we had in France, but instead a more modern one. So, now we want to hire a newer one to see how we like that before buying one. We also need to look into what it would be like to go on campervan holidays with babies and toddlers, because if it's just going to sit in the drive for a few years, we'll probably just wait.
I'm not sure where we'd go in Spain with it. One of the things we liked about our trip to France was going through the little villages that we wouldn't have normally seen on a regular holiday, so we want to do something similar in Spain.