Hi Sav,
Only kidding about the Birds!
I normally go every couple of years to the Manx and just book the vehicle as a van within the appropriate length. I can't recall being charged a commercial freight rate, but to be honest I never really looked at the booking fine detail. Last time we went I think the I was charged something like £350 return. Next year there's 4 or 5 of us going so I'll need a long wheelbase van which no doubt will put the rate up.
Looks like you had a good time.