Some things to consider on a cross country trip are comfort things connected to the range of temps you'll encounter, so a few more clothing options that add a bit of space.
sleeping bag, camp mat, I take a compact camp pillow cuz I value a good night's sleep, these three take up space in one of my rear panniers, not heavy but volume.
As you say, tent on top of rack is easiest, keeps wet tent away from stuff in panniers (dew in morning common, so damp tent)
Small stove and cooking set a real bonus as mentioned.
which leads us to these questions....Are you 20 or 60?
what camping have you done
how minimalist/uncomfortable do you either know or THINK you'll be fine with
I take a full rain gear set, good rain jacket, pants and rain shoe covers, rain helmet cover, this takes up space, but totally worth it. You may not think it's necessary, or rather, think that it's necessary, unless you've spent miserable, wet cold days riding when you didn't have this stuff.....again leads back to your misery acceptance and or real life experiences or not.
so add in camping gear, rain gear and even a small cooking kit, and your rear pannier only setup starts to get filled to the brim.
You'd be surprised how even little clothing additions can make the difference for warmth, comfort. For me it is stuff like a light toque (a beanie), a fleece neck up buff type thing, some thin gloves, warm wool socks, wool blend arm and leg warmers.......
heck I even bring dish washing gloves for those cool, raining all day crap days, if not your hands freeze.
the most important thing is that you practice putting equipment lists together, packing and riding with it to see what works for you, and or your misery acceptance level.