My Dad and Mom had a Jayco popup truck camper they got a lot of use out of before they upgraded to a travel trailer. Too bad you don't live in Eastern WA I think my Dad still has it and would probably let you have it for free.
Downsides were no grey water tank for water discharge. It had a plastic bag the sink drained into. And no toilet and black water tank, it had a spot for you to put a porta potty but it wouldn't hold much, although you would probably only use it at night anyways. When you park you will need to level your truck by stacking plastic things under 3 of your wheels.
Upsides working fridge, furnace, stove/oven and hot water heater all powered by propane. Cab overhead bed is comfortable and pretty specious. I believe there was a second bunk that would fold out over the table. Because it folds down you aren't pushing a lot of air when driving. Raising the roof wasn't too bad and could be done under 5 minutes. I don't think they could go in the camper unless it was in the truck bed.
I think it will be great for you and your girl. You will need to do something electrical to the truck as you will be charging off the truck and you need to be able to disconnect from the truck battery when camping. I think there were was a dedicated battery for the camper. You also need to add some braces to your truck to bolt the camper to.
This looks like what my parents had: http://blog.omnux.com/index.php/2006...-truck-camper/
Pickup a Honda EU1000 or EU2000 generator and a cheap TV/DVD combo unit and you can watch movies all night long and charge your battery.
Another big advantage other the Tent is you are able to stock your camper with paper plates, plastic forks and spoons, and other things. When you go camping you won't have this big list of things you need to load into your truck and you won't need to buy ice all the time and can cook without starting a fire.