During the build stage you will likely need a "commercial for personal use" policy. After the conversion is complete you can provide pics to DMV and your insurance to transfer it to an RV policy.
Most states require you have at least 4 of the following 6 items in the conversion. DMV will often take your word for completed conversion, your insurance won't. So if you get it registered as an RV, you'll have trouble insuring it for something it isn't.
(i) a cooking facility with an on-board fuel source;
(ii) a gas or electric refrigerator;
(iii) a toilet with exterior evacuation;
(iv) a heating or air conditioning system with an on-board power or fuel
source separate from the vehicle engine;
(v) a potable water supply system that includes at least a sink, a faucet,
and a water tank with an exterior service supply connection; or
(vi) a 110-125 volt electric power supply.
I Thank God That He Gifted Me with Common Sense