I have a Fiamma rack on my T4, so on a hatch style rear door, but the design of the barn door mounted version for a T5 is similar in use. Yes, it can be a heave to get heavier bikes on the higher style rack, but the Fiamma units are very secure on the door(s) and the bikes are held firmly in place. The barn doors of a T5 remain openable with the Fiamma rack and/or bikes in place. So, access to there rear interior is easy and convenient.

To put my bikes on the Fiamma, I pick up the frame about half way down and lift it, tilting the top toward and over my head while aiming the tyres for the rail. With the tyres in the rail, I tilt the bike up to vertical and attach the top arm to the cross bar. Once you have done this for the first time and have the top arm in the ideal place, it is easier and faster. Usually, one bike faces in each direction to allow them to nest pedals, handlebars, etc. I'm 5-8; you may find this a stretch a 5-+.

Thule make a rack for the T5 barn doors similar to the Fiamma. There is a video online of a guy installing the Thule rack and placing his bikes on it, opening the doors, etc. The Thule rack has locks available for the clamps that grip the crossbars of the bikes - a nice feature for basic security, although I'd personally do more for longer periods unattended or in high risk locations.

Installation of either rack is straightforward; I shouldn't think you need a professional installer. You may want to find someone who has one of these, or even a T4 version, to see if you can lift your bikes on to it comfortably. Perhaps a dealer can help with that, and installation, too.

Racks that go on tow bars are generally lower and easier for placing the bikes on them, but unless you get one that swings out of the way or drops down, you need to remove the bikes and maybe the rack, too, to open the doors. You may need to remove the bikes anyway, depending on how the loaded rack interferes with the doors, or with or without bikes on it. I would not purchase a tow bar mounted rack that I did not see functioning (bikes on, bikes off, doors open, etc.) in person or in a video, or one that I had strong positive reports on from real users - perhaps someone here who has one will chime in.

Tow bar racks have come a long way and there are now models that are better designed and made and are more secure. But there is a huge range of makes, features, and sadly still, quality.

 

I have the Fiamma 2 bike carrier for my T5 barn door. You will probably need a small set of steps to install it as it hooks over the top of the door.

There are four fixings, two top two bottom (which also hook around the door). The fifth fixing rests on the bumper.

I find it absolutely fine in terms of rigidity, and regularly have 2 adult bikes on it.

I have it mounted on the left hand rear door (the number plate isn't obscured) and both doors can still be opened (without bikes on).

I'm quite short and manage to lift the bikes up onto the rails, but a step would definitely help.

The bike is secured via 2 wheel straps and a crossbar strap.

Whoever you get to install it just be careful with the mounting brackets as if in the wrong position will mark the paintwork.

Carrying bikes is always a bit of a faff regardless of how you do it!

 

Personally I fitted a towbar and then bought an Atera Strada Evo 4 bike rack. This rack slides away so you can still open the doors with it attached. There aren't many racks that are suitable from the research I did.

 

Many thanks for the replies that's really helpful and that's good that the fiamma racks are very sturdy. Think I'll look into those first- now it's holiday season I might keep my eyes open in the local car park! (yes, that does sound odd...but just to get a sense of how high mounted they are.....I won't start trying to take other people's bikes off though!)