Here is what I am doing to secure my 16' conversion..
- Wheel boot that covers the lug nuts:
http://www.amazon.com/gp/product/B003E1 ... 00_details
- The best cargo trailer external locks I have found.. Don't lose the key.. These are pretty much cut proof as far as I can tell:
http://www.amazon.com/gp/product/B000W0 ... 01_details
-Full alarm system with digital tilt, field disturbance and 2-way paging (1 mile claimed range). Air horns and siren mounted under the floor boards and surrounded in a secure grating.
All screws that are used to attach hinges for doors are epoxy filled.. I was thinking about JB Weld but that is a little too permanent at this point.
This may be over the top for most but once completed, I'll have in excess of $70k in diving equipment inside alone.. I"m thinking a "Sewer Cleaning Service" wrap might be in order as well...

j/k!