Thanks @DaveR and @The escapist. Any chance of pics showing what reinforcing was done to the rear bar? Or a bit more of a description? I am not convinced with what I am proposing to fabricate in the above sketch that it would not work. I can understand attaching a tow hitch to the original bar only would be vulnerable to flex. But with the additional 2 rails of the RHS spaced at least 200mm apart and secured back to the main chassis of the van, I think it would be more than adequate handle the bounce of the bikes / rack.
Add an additional support of a strap (the non stretch type) secured to a solid part of the van can only further improve the strength.
Add an additional support of a strap (the non stretch type) secured to a solid part of the van can only further improve the strength.