Dom,
If you look at the pictures of mine with a KingCat inside, you will notice the 2" foam, and the velcro straps holding it in position. I have used this method in two trailers so far as it works! A friend has used the same method in his 24" trailer for several years and has experienced no problems whatever.

If you install a PVC cradle on the shelf you will lose some of the utility a shelf offers. You can move things around on the shelf to suit a change in contents as long as nothing is hard mounted.

The PVC cradle would have to be very well padded....the 2" foam pad is far superior to a piece of pipe insulation slid over a piece of PVC tubing.

Some people will swear by using the landing gear in transit, some don't.

I use the foam pad, and have had no damage at all. I protect the finish by placing a furniture pad over the airplane or installing the wing bags before stapping it down with the velcro
.
I bought the foam at the local JoAnne yardage store...they keep it in stock, and you can cut it very easily with a long sharp box knife and a straight edge. It comes in 4 x 8 foot sheets. A strip of double sided cloth tape on each end holds the foam in position.

The 20 foot car hauler cost around $6,000.00 new, which is less than any of the jets it contains. At that price, I think that the tandem axle trailer is a good bargain, because of the brakes, and the ride quality of the torsion axles.

Good luck on your installation........