Sorry to hear you're having this experience but it's a Roadtreak. Leaking is what they do.
Years ago I discovered the plywood under the bed in our '01 200 was rotting thanks to the rear window and taillight leaking. I took the wall liners off to dry them. I saved the plywood by patiently injecting epoxy into it. I coated the big wood cleats which hold up the edges of the bed with epoxy to protect them from future leaks. I set the edges of the plywood on spacers to create a gap between it and the cleats to allow water to drain rather than soak the plywood.
I discovered the drains in the taillights were clogged with dirt. The drain tubes had been made too long. The lower ends were resting on the body, impeding drainage. I snipped an inch off each one a cleaned them out with a stiff wire.
We remounted one of the side windows with plenty of caulk. The rear window was too much of a project, so we had an RV shop remount it. Within a couple of years both were leaking again. At least the water can freely drain now instead of wetting the plywood and the liner.
I suspect the big fiberglass body is not rigid enough to resist various twisting motions going down the road, leading to the window caulking eventually failing.
After every rainy episode I open the drain plugs. Anything you carry in the storage compartments either has to be waterproof or in a waterproof container.
Another leak source is the big rubber hinges on the storage doors. With use and sun exposure they crack. You can find threads about replacing them and where to get new hinges.
As for the steering, when the van was new it went down the road like a drunken whale. We installed a steering damper, Bilstein shocks, and supplemental air springs on the rear axle. The handling improved substantially. Now with more than 100,000 miles the steering is getting loose; I suspect there are a lot of worn parts that need replacing. If no equipment like that was installed on your van I'm not surprised that with 20+ years of use it's a not a fun driving machine.
Again I'm sorry you're having this experience but did you not inspect and drive the van before you bought it?