To put you in the picture and more info as possible, I have a 4mm SWA cable from the property CU to the summerhouse CU with 2 double socket on a ring mains + lights.The question is, I have a pergola behind the summerhouse which is all under cover with polycarbonate roofing sheets (no cable will be exposed to rain), I want to split the ring mains from the summerhouse to extend the ring with a JB in the roof area which is easily accessible and put in 2 more waterproof socket in the pergola area on the inside upright support (6"x3" timber) approx 500mm from ground level, can I carry on using t&e 2.5mm cable clip to the wood frame or put it in trunking or swa cable,flexible conduit etc, bearing in mind it's all undercover as the three sides are fenced off and only 1 side is open from entrance & no rain can get in.