Bulkheads are the best thing you can find, the stress riser thing its actually more stressful for you to try to get around it than for the hull itself, leave that problem to boats with a way bigger size. If you really cant sleep because of the thought then use a flexible material to build or fix the bulkheads in place, i used a lot foam covered with fiberglass so i could carve it to integrate something. Do drill a little hole in the center of the bulkhead, and dont worry, water wont flood the whole kayak because of that.

Internal hatches: i wouldnt dismiss them right away, they are useful to be able to store long items that couldnt go on deck, thats if you have them (so maybe its time to get a more compact tent). The fact is that they are ok on the rear but on the front bulkhead its a pain. So if you want to have bow and stern hatches just save time and keep them on deck.

Failing bulkheads... i sort of think that if you built a bulkhead that breaks off then you have probably built an entire hull that would break way before that bulkhead. If your hull its solid... then why the bulkhead shouldnt be?

The spray foam: wouldnt call it dumb idea, the fact is that it degrades with time and then will start absorbing water, it wont soak water like a sponge and eventually will absorb mostly if it sits in it but, still, it isnt a "spray and forgetabout it" thing. Its a good solution only if you make it removable (spray foam doesnt stick to some plastics like grocery bags for example so use that to line the ends before spraying, obviously get rid of the bag after) so that every now and then you can renew it.
At this point you have removable foam flotation, but we know of flotation bags, they work in the same way, they arent limited in size by your hatch opening or the "cargo" since you can deflate/inflate at will to different sizes, they will last a life and wont generate periodic "foam garbage", they are more useful than the foam even for other emergencies. Build them yourself and they will be cheap.
For a day playboat to be used as roughly as you can until its end and will never have the space needed sprayfoam its a great thing.

Bubblewrap: use it only to wrap the kayak with it if you are sending it somewhwere. The air effectively trapped in it its a very low volume and you will have always moisture in between.

Bulkheads, external hatches and a number of drybags to keep your various stuff in its likely the best way. And it doesnt hurt to have a flotation bag in the hatch, you never know, to plug an hole, a broken off end... stuff like that.

For the search, there is the search function but if you have troubles with that do a google search targeted to the kayakforum domain, its fast and easy.

: Option 1.
: Bulkheads and internal hatches (accessible from the cockpit)
: (+) Watertight bulkheads are the floatation standard.
: (+) Unlimited cargo-carrying potential.
: (+) No holes/leaky hatches on the deck.
: (+) Bulkheads strengthen the boat by stiffening the hull (according to some).

: (-) If a bulkhead/hatch fails 1/3 to 2/3 of boat fills with water.
: (-) Added weight to the boat
: (-) Bulkheads weaken the boat by creating stress points (according to some)

: ******
: Option 2.
: Sprayable insulation foam filling the bow and stern sections.
: (+) Permanent floatation that is always working no matter what
: (+) Light, cheap innovative solution that should be easy to
: "install"

: (-) Once in place the area left for cargo cannot be increased
: (-) Not sure how the foam will hold up in the long run.
: (-) Unorthodox solution (has anyone done it).

: *******
: Option 3.
: A few (2-4) cone-shaped and progressively larger rolls of bubble wrap
: encased in plastic tape (to hold the shape) and stuck in the bow and stern
: section.
: (+) The volume of floatation/cargo room may be changed by adding/removing
: cones.
: (+) Always works no matter what.
: (+) Light, cheap and easy to install.

: (-) Not sure how the cones will should up in the long run.
: (-) Unorthodox solution (has anyone done it).

: I am somehow attracted to option 3. I wonder if it has any "legs"
: in your opinion.

: -Tom

: PS. This website could really benefit from search functionality, perhaps all
: these questions have been asked (and answered) before)