We had friends who bought a Georgie Boy and shipped it from NY to Liverpool - around $4500 at the time. They had to pay taxes when it arrived in port and then it cost a far chunk to have it converted to UK regs - the worst part was installing the seat belts which did not meet UK requirements and ended up with a 6" * 10" steel plate fitted to the outside of the RV on both sides!
Added to the impracticality of driving a US spec RV on narrow UK roads and the $10 a gallon gas, it's cheaper and easier to buy a UK spec Class B+ on a Mercedes Sprinter chassis.