I spent months researching which option I should go with and was reluctant to spend the $800 on the ISI racks however in the I bought these and mounted them on the A Frame as per (http://www.isi-carriers.com/customers/rt/jayco-expanda-bike-rack.html) and I am so glad I didn't try a cheaper alternative.
Towing with the bikes on the A Frame is fantastic as you can keep a close eye on the bikes and know that they are secure while still being able to get access to the boot. We also go away riding in the winter months and we leave the bikes secured on the front of the A Frame and we sleep in the rear bed which has worked really well and if you buy the hitch attachment for the car it is really easy to put the rack on the car if you need to drive away from where you are camping to go for a ride.
My advise is to bite the bullet and buy the ISI system
Towing with the bikes on the A Frame is fantastic as you can keep a close eye on the bikes and know that they are secure while still being able to get access to the boot. We also go away riding in the winter months and we leave the bikes secured on the front of the A Frame and we sleep in the rear bed which has worked really well and if you buy the hitch attachment for the car it is really easy to put the rack on the car if you need to drive away from where you are camping to go for a ride.
My advise is to bite the bullet and buy the ISI system