To me it looks like the cracks are mostly from lifts. Are they supporting the upper section even when going down the road??
On mine the roof is supported all the way around by the bottom section.

I've always liked your pneumatic lift system and I feel like you probably just need to fix your leaky cylinders somehow and it will be good to go. Maybe since you'll have to redo your cylinders anyway you might be able to add more spreader area at the top.
Here is my lift system to maybe spark some ideas.
Some of the pictures/videos are not the current setup but the concept is the same.
Video:


This is the best video I have of the inside.
Video:

A video of it operating underneath.
Video:

The parts of the system are:
It has a front "crank axle" made out of 3/4" galvanized pipe. It has a handle on one end and is supported with eye bolts under the trailer that work as bushings. It has four holes drilled through it that the 4 lift cables pass through and are cable clamped once in proper adjustment. Since everything is driven by the same crank everything stays synced once adjusted properly.
The crank handle is a round stake used for concrete forms that fits perfectly in the 3/4" pipe. Its removable for going down the road but when you finish cranking it up you can "kickstand" it while you put in your inside supports. Yours having wood to support the pulleys you might even be able to just leave it hanging on the cables.

A rear "pulley axle" that just redirects the wire in the back.

The cables pass through the floor of the camper into the living space through homemade pipe cable bushings.

Then the cables run through pulleys supported in the wall. I used large metal spreader plates which weren't quite big enough for this hamfisted guerrilla and I squished my foam (when the top jammed and I didn't realize that is what was going on). It still works fine but looks terrible. You luckily have wood so you could attach the pulleys to the bottom of that.

Once the cable goes through the pulley it travels down to an attachment point on the top half. Two large through bolts on each side.
This is a picture of the cable run through the wall pulley and then to the attachment point with upper section sitting on the lower section.
