Hello,

does anyone have any suggestions for getting RKT to stick to the PVC in a structure of a figure... any suggestions/tips?

melted chocolate does the trick.. white or chocolate. whichever works in your situation.

Royal icing works well too.

I have used clear piping gel, Wilton makes it

so apply those to the pipe first then the RKT?

I would brush the PVC with clear piping gel and then apply the RKT to it. I don't know how long your PVC pipe is, but I would start at the bottom and work my way up the pipe.

does piping gel 'set' ? and thus hold it in place?

Piping gel does not set like royal icing does. It does not get hard. It is very sticky and it works more like a glue. When left to sit in open air, piping gel will get a "film" over the top of it. When I was at the Wilton School, we used a food processor to mix piping gel and gum paste. This made an edible "super glue".
HTH