My van has been converted to a race day van, ie sleeping accom in the front half and garage in the back half. Its been on the IOMSP at least 6 return trips this year without any problems. Now TT is near things have changed.
Any van booked on the boat will be put on the scales as per the booked ticked.
If you have booked for 3 passengers traveling on the ticket then they will also have to be in the van when put on the scales. an Iveco 35s12 GVW is 3500kgs, over this then your not be allowed entry.