Liability insurance should be no problem and you can probably get full coverage based on the value of the chassis. Covering the value of the conversion will be very difficult and likely expensive. You will likely need "agreed value" coverage which will require a professional appraisal and is usually much more expensive, dollar for dollar of coverage, than traditional comprehensive insurance. They may still turn you down because the risk of things like fire damage will skyrocket, in the eyes of the insurer, when wiring, ventilation and the like is installed by amateurs.