ok my thoughts here

you have 3 choices
a steelwork that will support the wooden frame the planks attach to
a steel work you attach battons to for the planks
or a virtualy dead flat steel structure you can affix directly to
the surrounding fence was for ideas of design or even trying to make the gate as invisable as you choose

wanted to know if the wood had to be vandal proof or just for cladding and hiding rather than direct security
other things you will have to keep in mind
the gate needs to be desighned with the cladding in mind
if the gate is ouward opening you won't be able to fully close the front
the hinges pivots will be exposed and there will be a say 2" or 3"gap as the material in front off the pivot point determins the distance the pivot point will be from the edge when the gates fully open