Caravan insurance for home build

I am building a little off road popup caravan out of epoxy composite with all the bells and whistles. It would cost in excess of $120,000 to replace it with a comparable branded upmarket van.

If it got damaged in a prang, I would more than likely repair it myself. If the damage was extensive, it would have to go to a shipright for repair. Any other stuff I can do myself. I don't need layup, motor fusion or anything like that.

I'd like to insure in the event of some calamity like fire, theft or a really big accident at the lowest possible premium. So I have called several insurance companies like CIL, NRMA and AAIMI to ask if I can get cover with a very large excess of say $10,000-$20,000 to minimise the premium. The best any of these can do is a $1,000 excess.

I insured my boat in this way some years ago and am wondering if anyone knows an insurance company that is more flexible on the excess.

Thanks in advance,
Keith