I knocked off their kit on the jetta 
In all honestly I could still do a trailing arm setup, no matter what axle I use. Like John said, make the slip mount up front based off the trans crossmember. Out back I would not attach it to the pumpkin, I would make plates and mount it off the axle tube, just to the side of the pumpkin. As long as there is room inside the oem tunnel. I dont want to get into moving floor sheet metal.
Cost to make a tube trailing arm would be probably the same as 2 ladder bars. Since the ladders need twice the joints, but are shorter where as the trailing arm is more tubing material but half the joints/bushings. I would still be making tubular and adjustable lower links and pan hard anyway, so its about the same price, who knows. No need to nickle and dime it to death.
To me its all about learning, R&D and doing. If I think it will work, I will try it. If it sucks, I can and do admit all the I told ya so’s, got no problem doing that… its worth it to me to give it a shot than not try at all.
Hell, if the car doesn’t sell when its done, I can try both solutions and test them side by side. You all know I like writing books in great detail. It would be a worthy tech article if I did.