Cap'n,
The original tank strap for the Rickman CR was rubber with bent thin wire ends that fit over the front mounting studs and the rear part that bolted to the battery box area. Those straps haven't been available for many years although I got lucky and found a NOS one for my current Rickman-Honda restoration. My first Rickman CR used a nylon strap with a plastic buckle, and wire mounts from an original strap. It worked well but looked a little strange.
You might want to consider having one made from leather belting or nylon webbing.
BTW, have you decided which tank maker you prefer? Holtworks? The Tank Shop? or
RR