No, you really need to get your anchor points out from under the truck. Nylon straps bearing against the body of the truck will quickly cut through them, or at the least mess up the sheetmetal.
That's a huge truck camper, you only want frame mounted tie-downs. No stake-pocket tiedown is going to work. There are really only two options for purchasing a tiedown system for this size camper: Torklift or Happijac.
As far as using ratchet straps instead of chain/turnbuckles, fastguns, etc, just make sure those straps are rated for the load you are using them for. While there are straps made that would work, I would just use the proper hardware that's made for the job. There's a reason most TC owners use the type of equipment we do. It's because it generally works best.
:):)
