I have a Northern Lite and have had older Bigfoots (Bigfeet??) in my shop. There is way less to go wrong with these campers than any other brands due to the construction. Obviously the appliances etc are the same and come with the same issues, but as PCE posted above, if they are maintained properly, you should be able to keep one for a lifetime. One of my friends recently bought a mid 80s Bigfoot, and aside from interior wear and tear, there was very little wrong with it. The interior wear was noticeable, but that’s due to the hillbilly that owned it, not the camper itself.
Adding power jacks is easy. Solar is too. You just need to run wires from your power source to each jack location, and from the roof to the solar controller, and then to your battery. I’ve been buying Renogy products for my solar installs, and have been very pleas3d with both the cost, and the quality. They now have flexible panels that you can attach to the roof using only a caulking bead. I do a bead around the perimeter, and then one across the panel about every 6”. So far I’ve never had one lift. This keeps you to only the single hole for cables penetrating the roof. Obviously you want a clean, dry dust free roof to adhere to. You can buy the panels, a controller, and all the wiring with connections attached on Amazon. You can also buy fittings to run your cables through the roof to keep the hole watertight.
If you find one that has leaked in the past, you will probably find some interior rot to deal with. But it shouldn’t be structural at all. Self leveling lap sealant around all the vents etc on the roof is part of your annual maintenance. If you keep it up, you should not have any leaks.