Truck bed camping is pretty much like sleeping in the back of an SUV, and I've spent way too much time doing that. It works and for me was super cheap since my first car was a gmc suburban, but it has major drawbacks.
First is that you're sacrificing space for hauling clothes, weapons, coolers, and other gear because you need about a 2.5×6 foot area to lay down. That's half of your space or better just gone. Even sleeping on a cot or building a platform so you can store stuff under you only gets you so much because at most you can have a foot of vertical space without mashing yourself into the roof.
2nd is that it's a pain and a half to have to get dressed and cook/eat if the weather is less than pristine. Crawling into the back of a truck when it's raining and cold to try and shed wet clothes and muddy boots in the area you're sleeping sucks the first night and REALLY sucks the 2nd night.
Like I said, I've done it a lot. It works good for quick hunts and overnight scouting trips when the weather is nice. But I got to the point where instead of setting up the rear for sleeping I just leaned the seat back. If you've got money for a camper shell you've got the money to buy a canopy tent and actually be comfortable, and it takes all of 5 minutes to set that up solo. Me and a buddy can both sleep comfortable on cots with some 3" thick memory foam pads, and in the morning we can stand up, stretch, and get dressed and have breakfast even if it's pouring rain. If we've got electricity i have a heater, a box fan or two, a boot dryer, and a cord to charge phones and other goodies.
