I find that a 9" centerline cataraft frame height is optimum if one intends to use ammo boxes in the cargo array.
Ammo boxes are heavy, cheap and define the poor rafters dry box. Ammo box arrays make good seat platforms when covered with a pedro pad. Ammo boxes usually float and are a true "Dry Box"...Bone dry; rarely leak.
For frame widths in the 72" to 50"range, an 8" centerline height is mighty nice. This height will give you the lateral stiffness you need and the underframe clearance for cat tubes down to 20".
For frame widths in the sub 50"range, an 7" centerline height is ideal. This height will give you the underframe clearance for tubes in the 20" to 18" range. Ditto for 6" CL on 14-16 range.
For self bailing rafts, the same set of selection criteria applies. Suspending your cargo on a cat chassis cross bar
frees the floor to do what floors do. Suspending your cargo on a cat cross bar prevents the pinch point between cargo and the floor.
Re: Car Top Cat Chassis
Yup, they make good car top carriers. However, they change the inertial characteriatics of the vehicle. If you have 500 lbs on the roof of a VW Jetta, you had better not be running figure eight.
Use Loop Straps For CataRaft Rigging. Loop Straps offer the one buckle solution to the attachment of the d-ring set to the frame. This allows outboard d-rigging when the boat inverts and also add strength to the frame.
The upper limit of length between the cat yokes is 82". If you are going longer than 82", add a third yoke; fourth yoke for 120" plus. There is no rule that say the yoke height has to be constant across the length of the craft. RowFrame Yokes generally include setscrew fittings and these fitting allow vertically curved frames allowing a taper fit to some raft geometry.
RowFrame does scaled cross sections at no charge, just state your assumptions.