Don't want to put a damper on this (we do motortrade policies) but you do have to be trading of some description, buying and selling 5 cars a year is enough for some companies.
BUT If the worst happens you may only be paid out TRADE price.
Also modifications are not automatically covered on the majority of policies - the terms of the policy are written slightly different to a standard motor policy, they can make it a material fact if you change anything on the car you will have to tell them.
Be aware also that some road risks policies dont cover the cars at the trade premises (home address if you work from home) or within 1/4 of a mile of these premises if parked/stolen
If you want anymore info mail me
Jeremy