Welcome to RVForum.net. We have several UK members here and perhaps one of them will offer the wisdom of their expereinces in buying an RV in the USA.
I'd be very careful of PPL. I've heard some stories of dealings with them that lead me to believe their sales organization promises a lot more than they typically deliver. The really negative reports I have seen came from people who were rather naive about dealing with RV dealers and so got taken in by the hype and glib assurances that everything would be wonderful. Since you are at a disadvantage when dealing from the UK, and perhaps are a first time buyer as well, you are pprobably more at risk than most. If they have something that seems perfect for you, make sure you get prices and commitments in writing and don't tie up a lot of money in a purchase deposit before you get there and can see the rig for yourself. And make sure any deposit is refundable.