Hi Brendan,

This is quite a tricky one and I'd urge you to contact Revenue about it yourself for clarification before bringing the vehicle over the border. 

One thing for sure is that you'll have to pay VRT at the full amount, which will be 13.3 per cent of the OMSP. That's the Open Market Selling Price as determined by Revenue. The rate drops if it's an electric motorhome, but that's not very likely to be the case. 

Assuming it's new, VAT should also be payable, though usually VAT - at 23 per cent - is calculated according to the purchase price of the vehicle, and you didn't technically buy it. This is where the clarification is needed, as Revenue may decide to charge VAT on the OMSP instead of the theoretical price of the vehicle in the North. 

Customs duty shouldn't be payable so long as the vehicle was "customs cleared" in the North, but you will need paperwork to prove that.