Thanks for the replies to my questions.
After careful reading of this thread and other threads I found through forum search, these are my conclusions.
Some people use horse mats and it works well for them. Some people use DeeZee type rubber truck mats and it works well for them.
Horse mats have the disadvantage that they weight 80 lbs so can be hard for one person to handle, for example to take out of the truck to clean the bed. Also it is a do it yourself job for the initial install to cut the mats and glue together pieces. A DeeZee mat weighs 58 lbs and it is sized to the truck so you just roll it onto the truck bed. So since people have had success with DeeZee mats and it is easier, I placed order for a DeeZee, around $95 on Amazon.
The next topic is spray in bedliner. The consensus seems to be definitely a rubber bad mat either DeeZee or horse stall mat. Then it seems many people put the rubber mat on top of a spray in bed liner. But there were some posts to this thread that clearly said people had success with a rubber bed mat without a spray in bet liner.
For me, the truck is strictly to haul the camper. I will probably never carry any significant other type of cargo. So a professionally installed LineX or Rhino spray in bedliner which seems to cost around $450 seems excessive. But HercuLiner is a do it yourself project that costs less than $100, which would seem to be about right for my use.
A spray in bedliner will keep the rubber mat from shifting against the truck bed. Someone described the do it yourself HercuLiner as essentially thick paint with rubber particles which works well to keep the bed mat from sliding.
But again, if it will work without a spray in bedliner as some said they have had success with, why bother with the spray in bedliner?
It would seem to make sense to first try the rubber bed mat without a spray in bed liner. If the mat shifts against the truck then I can add the HercuLiner bedliner. If the bed mat does not shift, I am unclear why to add the HercuLiner. My understanding is that a contractor hauling cargo would want a spray in bedliner to protect the truck bed, but if my only cargo is the camper I can't see why to add a spray in bedliner except if it turns out to be necessary to prevent shifting of the bed mat against the truck.
Then the other type of potential shifting is the truck camper against the rubber bed mat. Most people say the rubber bed mat is enough for them. Others do have problems with shifting. Usually the tie downs prevent shifting front to back, but some have problems with shifting side to side.
It is becomes necessary, shift of the camper is usually controlled by boards between the camper and the truck wheel wells, or a cut up pool noodle used as a wedge again between the camper and the wheel well.
www.rv.net/forum/index.cfm/fuseaction/thread/tid/28328708/srt/pa/pging/1/page/6.cfm
Or in the above page hedgehopper shows a picture of a wood jig he build that looks like something to stay in the truck bed permanently. Looks very nice as a permanent solution rather than inserting boards every time you load the camper.
I hope the above helps to summarize this topic. Realize that so far I have zero experience since I am currently setting up my first truck camper. The above is only summary and conclusions from careful reading.
Comments are welcome. Also I have the one open question above. Why I would want to consider a spray in bedliner unless experience becomes that the bed mat is shifting without it?