Bike rack for electric bikes on a Fairford

I own a 2019 registered Fairford (based on a long-wheelbase Peugeot).  I currently have a bike rack for two pushbikes hung from one of the rear doors which is adequate for those bicycles.  However we are envisaging buying electric bikes which, of course, are much heavier.  I'm sure the existing bike rack will not suffice.  The alternative seems to be to have a tow bar fitted with a bike rack mounted on this.  There are various designs.  Of course the bike rack and electric bikes will collectively be heavy, even with the batteries removed and transported inside the van.  I am concerned that the weight on the back of the van could cause instability.  What about the overall load weight of the van.  

Any observations or advice would be gratefully received?  Have any other owners of Fairfords, or similar vans researched this issue?

I’ve just done exactly the transition you describe to our fairford, and now have a tow bar and a Thule velospace electric bike rack. We also updated the van from 3500 to 3900kgs to stay the correct side of the law. The physical components of the van remain the same (no modifications required) but we can now travel without having to give too much consideration to our payload.
We struggled to get a tow bar fitter to commit to the job as our gas pipes were in the way of the tow bar mounting points on the vehicle, I ended up doing it myself at home and then taking the vehicle back to the tow bar fitting depot for the job to be finished.

Thanks, that's useful.  From what you say it seems that the van handles OK with the extra weight on the back?

No issues at all

Have a Kingham with towball and Thule Strada rack. Carry 2 electric bikes with no issues and can slide them out of way to open rear doors