There is also a growing number of bad news stories in the RC sub world about the longevity of these sub kits.
Here is one but example: a 3D printed I400 sub. This one wasn't left in the sun but stored in a shed - which heated up. (Not mine).
One of the key issues with RC sub kits is that in wanting to fit a removable / accessible water-tight cylinder (WTC) as the subs working innards means that RC subs don't lend themselves to affording themselves of the real estate required to have the same level of cross bracing / stringer reinforcement that a model ship has. A good GRP sub kit, and I have built many, doesn't require such reinforcement.
Here you can see that this 3D printed kit is completed naffed. I am not sure whether reinforcing would have resulted in a different outcome?
There are a couple of manufacturers that I know of that are using 3D printing to make plugs which then in turn are used to make GRP moulds and then GRP hulls. A higher cost of production but perhaps a better way of using 3D printing to create a more stable end product.