Are solar panels cost-effective

Smaller panels are one way to go; see this article Hail Damage and your Solar Panels:

If you decide to install photovoltaic modules and worry about hail damage, there are a couple of things to consider. One of the most important concerns the size of the modules. If the region you live in is subject to frequent or serious hail storms, smaller modules are easier and less costly to replace. Also if a large module sustains damage, it will seriously reduce the power output, or even cause the system to fail completely. The drawback with using smaller modules is that they are often more expensive to install.

But of course there is not much that would withstand very large size hail but then your home insurance should cover the damage (just like the damage that would happen to your car and/or house during one of those hail storms). I do not think it is very expensive to get your solar panels added onto your home insurance policy (if they are not covered already). See this answer too: Do roof solar panels and hail mix?

Stacking the panels on top of each other should be fine, but I would not suggest stacking all off them on top of each other as the bottom one will have to bear tremendous weight and might warp it.

Try and place wooden battens (for air flow to stop moisture from being trapped and help displace weight evenly to the next panel using a soft surface) between panels on the same frame that they were mounted to the roof. The frame is load bearing and will handle weight on top of it and disperse weight downwards to the next panel.

You do not have to cover each one in bubble wrap. Just stack em using batons(bareing in mind weight) and then cover the entire stack in foil and possibly some polystyrene and or bubble wrap on the corners and top to prevent shock damage in case something hits or falls on it.. you never know.

Some panels you can stack ontop of each other with no problem as they have a robust frame that supports all the weight.

Exercise some common sense in how to stack them. Make sure they are level and aligned. check on them every now and again during storage phase in case the weight makes something give in.