Stifler,
It will take an hour or two to take the whole back end off - its very straight forward. With that removed a 6 will fit in a 20' container with prop still attached (although best to remove it to prevent damage). I suggest that you contact someone in England who has imported an RV before, I would recommend David Hockings at Cristal Air on 01323 811779. Has has contacts in Wisconsin who can dismantle and pack the aeroplane. It could easily cost £3 or 4,000 to get the aeroplane landed in the UK, plus re-assembly and certification charges.
The most significant headache you will have is to get a permit. Using someone who has done it before will be a huge advantage. If you haven't already bought the RV make sure it conforms to the drawings and that the engine has at least an A&P mechanics' signature in the logbook the last time the bottom end was apart (very important) before you buy. If it is modified it will take much longer to get a permit and the LAA might insist that you remove the mods. If you have already bought it, and it is modified, then ship spares that might be required in the container - it will reduce the costs of the parts by at least 50%.
In any event it could take 6 months to get a permit.
Pete
PS I wouldn't bother with Denmark, they have caught onto the VAT scam and it will be a huge hassle to get the aeroplane to the UK, if you aren't a US citizen you won't be able to register the aeroplane in your name and so can't fly it on its US registration.