Looking at the video that should be OK on the other hand HYMER may have put fixing points within the wall to drill into Hymer should be able to tell you.
Could well have fixing points I will try emailing them but not sure if I will get a answer I think in the mean time I am going to order the rack and have a look things always seem easier when you have the parts in front of you.
If all else fails I can always get someone to fit