Can I take one of my Directv boxes and use in camper

So long as it is not a client you can use it for a period of time until it misses the authorization code from the sat.  For longer periods you need a SWM slimline dish on a tripod or sled mount and a power inserter.  You will lose all local channels when you get outside of the spot beam.

Box must be H or HR model.

Need slimline SWM dish on tripod/sled mount or Winegard Trav'ler.

Once outside home spot beam will not have locals.

If you have the Genie-2 (HS17) then you are out of luck. It only allows Clients which cannot work standalone.

You can take an HS17 and a mini camping if you wanted to.

Yes but it is more hassle to take multiple boxes and then have to set your service back up at home. Also anyone at home is without service as the HS17 runs everything.

It is against the TOS to be using the same account in two locations at the same time.

By intention, that is to prevent having two residences (account sharing) which violates locals, RSNs, and taxes to be paid.

Taking a box for temp travel, isn't a big issue, especially since outside of spot beam you cannot locals and RSNs anyway.

Now those who have a "vacation" home and didn't deactivate/reactivate the appropriate boxes, and update physical service address accordingly, was a huge hole in those policies which is why AT&T stopped the seasonal/vacation disconnect of boxes and reactivation of used boxes.

So long as the box in question is not being used "permanently" at another address, then the OP is fine. Especially since satellite service is on-way without GPS tracking.