The struts are for the Tailgate (there on the outside edge of the door and inside the tailgate jam (if that make sense - like normal cars), many guys on here use an SGS engineering in Derby (on the outskirts) should their struts need a regas or replacement - I believe that they are very good.
I have a Fiamma Rack and my struts didn't need regas or anything, but I did get a spare set for my parts from evilbay for £12 inc postage..

so at least if mine fail I have a back up set so that my others can be regassed
There is an alternative strut that is uprated but it is a bit shorter than the original ones from RS, there about £70 the pair , do a search on here to get the info