Cyclist and caravanner here
Transporting the bikes is a real nuisance. Normally end up with one, or two at a push, on the spare wheel carrier on the back of the car (4X4) and one or two in the van.
It's far from ideal though, there's a fair chance of damaging the interior of the van and it's a real faff getting them in and out with all the rest of the gear inside.
Did consider the roof mounted carriers but the car is a bit tall to easily reach the roof and fuel economy is bad enough as it is whilst towing.