Hi there, are you good with car electrics? It all looks very complicated to me! Anyway, the 13 pin system is totally superior to the 2 x 7 system, better connection, much neater. All the new caravans are now coming with it as standard. Try Googling for it, there is lots of info, also look at Volvo Owners club website. The use of the correct cable (5 x 2.5 sq mm cores) is essential.
The detachable bars really are worth the extra money, very neat, no danger to shins! It will require a small cut out in the bit below the bumper, so not totally invisible. I think the Volvo one is supplied by Brink, so no doubt it is available for a lot less than Volvo charge. We bargained a good deal on ours from our Volvo dealer so had them fit it all.
If you decide to get one fitted INSIST that it is fully wired, some places leave some pins unconnected.