There's only two of us and Mrs F does not cycle. I put down the rear seats and carry the bike in a bike bag either laid down or upright.. A bike bag is a specialized bag that is designed for air travel so that other luggage is not damaged e.g. scratched or smeared with chain oil in the plane's hold. On site I store both bike and bag under the van.
I always partially dismantle the bike - eg remove wheels, mudguards and pedals.
If we still had children with us i would put the bikes on the roof. I'd be nervous about both the weight and the potential for damage to cupboards etc. One poster who owns a Hobby suggested carrying bikes on the rear wall. Fine for the Hobby, but I'm pretty sure that this is not possible on your average british caravan - wall is too weak
Try "carabyke"-it's a purpose made post with arms which clamps between the beds at floor level to prevent movement and which has arms to support the bikes parallel with the front beds. Don't carry bikes on the tow bar!
Just a cautionery note we use a towball mounted bike rack with the mounting sandwiched between the towball+bracket,we go to a site where at reception you book in and make a tight l/hand turn(full lock)last year i saw a van crush the bikes+damage the corner of the van,but it is a easy way to carry the bikes,even though you we can't get in the boot of our x trail with the bikes on.
We have put our grandsons bike inside the van, we wrap it with bubble wrap and lie it down in the middle, and prop boxes or the awning bag all around to stop it moving, so far we havn't sustained any damage or oil getting on the carpet, you just have to spend a bit of time moving items around, the bike was well cushioned with things that it just couldn't move.
Try "carabyke"-it's a purpose made post with arms which clamps between the beds at floor level to prevent movement and which has arms to support the bikes parallel with the front beds. Don't carry bikes on the tow bar!