You mentioned using an Otterbox case with the iPad.
The problem I see with waterproof/water resistant cases for iPads is that iPads tend to generate more heat from the back than an iPhone or iPod Touch, partly due to the size of the rechargeable Lithium-ion battery and overall use of the iPad, especially when playing hardware/software resource intensive games or other computer resource intensive apps.
The battery, CPU and GPU can heat up similarly to how a laptop or desktop computer components can heat up more doing more computing intensive tasks.
So, using a a waterproof, sealed-up case is that it is also an “air-flow proof” case, with no way for any open air circulation/venting of heat from inside of the case, trapping in any heat that the iPad generates with no way to vent the heat out to cool down the iPad.
If you take the iPad out of the Otterbox case when it is, relatively, still warm/hot from being inside of the sealed case, I am going to state there is the chance the differential of temperatures from inside of the Otterbox case and the outside air temp of the external environment might be sufficient enough to cause the one-piece, thin, aluminum back case to kink or bend in any way or fashion.
One of the reasons that if you use a waterproof case for an iPad, that you always need to completely take the whole iPad out of the sealed-up case when charging the iPad..
Just make sure the temps inside and outside of the case are fairly close to the same ambient temperatures.
I have read of these types of similar scenarios happening right here in these iPad support communities.
This is why I prefer just regular types of iPad cases and if I am going to take my iPad outside or in a laptop/computer bag or backpack and there is any chance of rain, I carry an appropriate sized zip lock/slide lock freezer style bag and put my entire iPad ( case and all ) into the freezer bag and sealed it until I can get my iPad into a dry environment, then take it out of the plastic freezer bag.
Also, I keep the power block in a separate area away from direct contact of my iPad/s so the block isn’t banging around anywhere near my iPad/s.
I, also, do this, so not to have something small and bulky pushing against my iPad/s that could act as a fulcrum, inside of the bag, to push against my iPad and, possibly, be a cause to kink or bend my iPad/s.