Hi John.
You certainly can use your sky card and system while in the caravan.
I have adapted my Lidle mobile sky kit to accept my sky plus LNB reciever and it works brilliantly even with the tiny plastic dish that came with the briefcase sized kit. We ahve no trouble setting up. We use the compass on the back of the dish to point it roughly at Astra 28 east. Then we use the system set up facility on the sky plus box to finalise the signal strength. It is a little fidly getting two good signals. Sky will work on a single good signal but you won't have the sky plus record and watch facility then.
As we are currently using our tourer as our home, I have got the system set to full efficiency, so that her majesty can watch and record.
One tip I can recomend is to use an inverter to power your sky plus box from the caravan 12V supply. We have done this as our mower girl seems to pick the day we go out to unplug the electric to do the grass cutting, which used to delete the recording menu for the day. with the inverter, we have solved that issue. The inverter cost us