At this point look at as many truck campers as possible so that you have a general idea what you want and what you are willing to for go.
If you are looking at a truck camper with a slide out have the owner or business pull the slide in... that way you can see if the camper is useable with the slide in... can you get to the bathroom if you need to go in a hurry.... would the slide be in a traffic lane if you have to put it out and you are parked along side a highway.... ???
Once you have an idea as to size and features you want in your truck camper you'll have to choose the truck that can haul it... not one that has to have a lot of modifications to beef it up. When you try to modify a truck to reach a proper capacity there will always be a weak link somewhere.good luck and have fun