I'm with you regarding not cooking in the trailer. We do almost all food prep, cooking, eating and cleanup outdoors; still making adjustments so we can grab all supplies and step outside. Will add a rear hatch to store the portable stove under the rear bench with access at the outdoor curb side. Likely will store other cooking equipment there as well. Also we always plan really simple meals and sometimes have food pre-made in the frig -- either cold meals or ready to heat -- this is especially nice after a long drive to campsite.
Which gets me thinking... cooking/eating indoors vs. outdoors is as individual as many other things. Some would never have a camper without a bathroom, but we opted for none. Love the extra storage space! Especially since the addition of a child made the 13-footer too cramped (it's not the people, it's all the gear). The porta-potty works good for us (mostly for night time and for child) and around here state campground bathrooms are very clean (we wear flip-flops just the same), and never run out of hot water; and truck stops offer amazing full private baths for $5. We only shower in the campground baths and do all our dressing, hairdrying, etc. in the camper so we don't haul much to the baths. (Each of us has a pre-stocked cloth bag.) And if it comes down to it we feel sponge baths are about as comfortable as the tiny bathrooms and small water heater capacities in small trailers. If you don't know if you are a must-have-a-bathroom type or not, may I suggest you rent or borrow a trailer similar to what you are designing? Trailer showering is not at all like showering at home.
You might find the additional storage space outweighs your desire for a private bathroom (remember a water heater takes a chunk of room as well; we have an electric teapot that heats a good quantity of water to boiling in about a minute). One of the things I detest is having to move items before I can find the item I need so really appreciate good storage and organization. If you detest campground baths, then stick with designing a bathroom that works for you and your family. We opt for our needs and seldom worry about re-sale; if you don't design too much out of "ordinary" you'll find like-minded buyers when the time comes.
Have fun with your build!